Pizza Styles According to Serious Eats:

Neapolitan



Small (about 10-inch diameter), thin-crust pizzas made in a
wood-burning oven. Usually have a puffy "cornicione" (lip or end crust)
and marked by use of the freshest ingredients applied sparingly for a
careful balance. Perhaps the most popular is the pizza
Margherita—topped with fresh sauce made from San Marzano tomatoes,
fresh buffalo mozzarella or fior di latte, and a little bit of basil.
Other traditional variations include the marinara (just sauce and maybe
a sprinkling of an aged cheese) or the Napoletana (a marinara pie with
anchovies). This style, of course, is known the world over.

Related



Naples Pizza Photo Gallery [Slice]
Naples: Pizza at Its Source [Slice]

New York–Neapolitan



Once the Italian immigrants brought their Naples-style pies to the
States, it evolved a bit in the Italian neighborhoods of New York to
something I've seen referred to as "New York–Neapolitan." This is
basically what all the coal-oven
pizzerias of New York serve. It follows the tenets of Neapolitan style
in that it's thin-crusted, cooked in an ultra-hot oven, and uses a
judicious amount of cheese and sauce (sauce which is typically fresh
San Marzano tomatoes, as in Naples). It deviates from Naples-style in
that it's typically larger, a tad thinner, and more crisp. New
York–Neapolitan is rarely found outside New York City. However, I
believe this style eventually evolved into ...

New York–Style



The round, thin-crust stuff that most people in the U.S. think of as
"pizza." And don't anyone give me guff on this. Go ahead and think of a
pizza. Nine out of ten of you thought of something round and more on
the thin side than the thick side, right? Even the major chain stuff,
with all their variations in crust style, I'd say that their default
pizza is closer to regular NY-style than, say, deep dish or Sicilian or
what not. A true New York–style pizza ideally has a crust that's at
once crisp and chewy. Can be topped with whatever you want
but is best with only one or two toppings applied (so crust remains
crisp). New Yorkers generally fold it while eating. Also referred to in
New York as a "regular" pie or a "regular" slice. The default regular
slice is a "plain" slice, i.e., no toppings, only cheese.

Sicilian-Style



A rectangular pizza with a thick crust. Cheese may or may not appear under
the sauce, though it's my understanding that Sicilian traditionally
used to feature the cheese under the sauce. Often marked by the strong
presence of garlic. Also known as a "square slice," because it's cut
into squares (or rectangular shapes close enough to square to merit the
name). Usually the same price or a quarter more than a regular slice,
so get this if you're broke and hungry. Doesn't seem to be as popular
in New York as the regular slices and pies, primarily because only a
few places really do square pies right. Those places are treasures and
should be appreciated.

Grandma-Style (aka 'Nonna Pizza')



Essentially a thin-crust Sicilian. I've gotten guff for saying that
in the past, so if any of you out there want to correct me and argue
for a workable definition of this style, please comment. It was sort of
a Long Island thing until the past couple of years, when it started
making inroads into the boroughs of New York City. Typically has a
fresh, lightly seasoned sauce.

New Haven–Style



Cooked in a coal oven, has a very crisp crust that is thin but still
typically thicker than New York pizzas. Marked by a characteristic
oblong shape, often served on a sheet of waxed paper atop a plastic
cafeteria tray. Thought to be the place where clam pizza was developed
(Frank Pepe's). The two biggies here are Sally's and Pepe's, but there
are others (notably Modern) with their adherents. New Haven partisans
often argue that pizza was invented here, but I believe NYC has them
beat on this claim.

Grilled Pizza



Grilled pizza was invented in Providence, Rhode Island, by George Germon at Al Forno.
Grilled pizza has a thin crust and is cooked quickly—directly on the
grate of a grill. Contrary to what you'd think, it does not fall
through the grate, instead setting up quickly over the intense heat
before being flipped and topped with sauce and thinly sliced toppings.
(Toppings must be thin so they heat through in the short time—typically
a minute a side. Sausage or anything needing thorough cooking need to
be prepped beforehand.)

Grilled pizza has since moved beyond Providence—there are at least
five such pizzerias in New York City, and the in the last three or so
years we've seen this dish move from obscurity to backyard grills
nationwide, thanks to the annual grilling coverage in magazines and
newspaper food sections that crops up around Memorial Day.

Related



Grilled Pizza archives [Slice]
Grilled pizza [Wikipedia]

Bar Pizza



Ed Levine goes into this in his book, and you can read an excerpt about bar pizza on Slice.
Ed says, "It's usually very thin-crusted to (I'm guessing) leave plenty
of room in the eater's stomach for beer. It's baked in a gas oven that
may have replaced a coal oven if the bar is old enough. Bar pizza is
made with decent, commercial, aged mozzarella and comes topped with
canned mushrooms, standard pepperoni and, if you're lucky, house-made
sausage." The bar pizza Ed describes and that I've had is very similar
to something I call "Midwest-style pizza."

Trenton Tomato Pies



In the capital city of New Jersey, pizza does not exist. Here,
they're known as "tomato pies." As Slice correspondent Rich DeFabritus
wrote in his review of the two dueling DeLorenzo's
there, "There is a body of myth and lore attempting to distinguish
tomato pie from pizza. The generally accepted explanation is that a
tomato pie is built as follows: dough, cheese, toppings, and then
sauce." Trenton tomato pies would then seem to have much in common with
a sauce-last grandma pie or a Detroit-style pizza, but tomato pies are
round.

Old Forge–Style



I know the least about Old Forge–style pizza but am including it here in the interest of providing a wide range of styles. On Pizzamaking.com, user IlPizzaiolo describes it thusly:
"My friend studied a type of pizza from Pennsylvania that sounds close
to what they are talking about. It is like a medium-thin Sicilian
dough, the pan oiled with peanut oil, so the dough sort of got a fried
consistancy like pan pizza from Pizza Hut. The cheese [was 100%
Wisconsin white cheddar.]" I think I need to take a three-day weekend
and investigate Old Forge pizza.

Detroit-Style



I don't think I was even aware of a "Detroit-style" pizza until digging in and doing some research on this topic, but Wikipedia has an entry on it,
where it is so described: "... very close to the Sicilian-style pizzas,
or is also known in other places as 'Italian bakery style pizza'. It is
a square pizza, with a thick deep-dish crust (sometimes twice baked),
and with sauce put on the pizza last."

Related



West Michigan Pizza: Fricano's and Mr. Scrib's [Slice]
Detroit-style pizza [Wikipedia]

Deep Dish



I don't know if I need to elaborate much on deep dish, since, like
New York–style, you already know what it's about. And I'm not trying to
knock it here, but it is more like a casserole than, say, focaccia.
It's cooked in a deep pan, with a deep, thick, buttery crust, and a
chunky tomato sauce. Lots of cheese, lots of (and/or copious amounts
of) toppings.

The crust is parbaked in the pan before toppings are added, usually
a layer of sliced mozzarella, followed by meats and veggies, then
sauce, then grated cheese. Unlike New York–style, it's eaten with a
knife and fork. How 'bout a neat little clip from a story in the July
20, 1997, edition of the Chicago Tribune:

Chicago-style pizza may owe its existence to a bad
enchilada. When partners Ike Sewell and Ric Riccardo planned to open a
restaurant, Sewell, a native Texan, wanted to feature Mexican food. But
one of the sample meals the partners tested made Riccardo so sick that
he rejected Mexican food entirely. Riccardo suggested pizza, which he
had encountered in Italy--as indeed many American servicemen were doing
during World War II. Sewell's complaint with pizza was that it was
insubstantial, little more than an appetizer--and readily available in
Chicago's Little Italy neighborhood besides. Sewell wanted a
substantial, meal-size pizza. After some experimenting, the partners
devised something with a thick crust and plenty of cheese. Pizzeria Uno
opened on this date at the corner of Ohio Street and Wabash Avenue.
Chicago has contributed many dishes to American cuisine, among them
shrimp DeJonghe, chicken Vesuvio and the Italian beef sandwich. But
none has been so widely imitated, nor so closely identified with the
city, as Chicago-style pizza. Pizzeria Uno, however, was not an
overnight success. In the early days, bartenders distributed free
sample slices to introduce customers to the new pizza. "Fortunately,"
Sewell said, "we had a very good bar business."

Like Neapolitan–style and New York–style, deep dish has traveled far
from its birthplace. Although, with a few notable exceptions, good deep dish is still hard to find outside Chicago.

Stuffed Pizza



Another Chicago specialty that is often confused with deep dish
because of its similarity. It's assembled and cooked in a similar
manner to deep dish, but it has a top layer of crust and is usually
taller and more densely packed with toppings.

Chicago Thin Crust



Another form of pizza prevalent in Chicago, though it seems that
folks outside the Windy City mostly overlook this style when talking
about Chicago pizza. It's thinner than New York–style and crunchier,
though it's also more tender and flaky. Almost pastry-like. I think
this crust style of this pizza has much in common with the bar pizza or
tavern pizza I've had in New York City and also with the independent
pizzeria pizzas I've had in Milwaukee. The Chicago thin-crust has a
smooth, highly seasoned sauce. Toppings are added under the cheese,
which is typically mozzarella. Often cut into a grid of square pieces
(instead of pie-shaped wedges) in what's known as the "party cut" or
"tavern cut." (See also "Midwest-style," below.)

Midwest-Style



Variations, I believe, are found throughout the Midwest—from Ohio to
Milwaukee to Chicago to wherever. I'd even go so far as to say that the
"Chicago-style" pizza just above is really a variation of
"Midwest-style." The Midwest style is round, thin, very crisp yet
tender-flaky, and is party- or tavern-cut into the grid. Sauces and
topping preference may differ from city to city and region to region,
but this style seems to crop up often in the heartland.

Saint Louis–Style



Might be mistaken for a Chicago thin crust at first, just on
looks—and maybe for the fact that Saint Louis and Chicago are only a
few hundred miles apart. But this style's very thin, crackerlike crust
is unleavened. And it's topped with a special three-cheese
blend (provolone, Swiss, white cheddar) called Provel that's used in
place of mozzarella (and sometimes, but not often, in addition to
mozzarella). Like Chicago thin crust, it's usually done party cut. Imo's Pizza is thought to be the originator.

Related



Imo's Pizza [Slice]
Saint Louis–style pizza [Wikipedia]

California-Style



The crust is more a vehicle for unique toppings and striking flavor
combinations not typically found in Italian cuisine—say goat cheese, or
avocado, or egg. Given California's access to produce, fresh vegetables
often make an appearance. Ed LaDou,
who made California pizza famous at Spago in Los Angeles and then later
developed the original menu at California Pizza Kitchen, is typically
thought of as its inventor.

And even though I think this might be a variation of the Midwest-style, I like the description of the following ...

Ohio Valley–Style



If Trenton can have a style based on a couple places why can't the Ohio Valley? Here, the blog Mine Road describes it:
"The first thing that you’ll notice that is odd about our favorite
pizza is that it’s square. Square as in it’s made in a square pan and
then cut into square pieces. Then you’ll notice that the cheese isn’t
melted all the way. The uncooked toppings are put on after the sauce,
base cheese (minimal), and dough are cooked. You always have to make
sure to have a slice ASAP before everything melts on the drive/walk
back to your place. You’ll also notice that our pizza sauce isn’t
really much of a sauce at all as much as it is just stewed tomatoes.
Also the crust is a mix between a deep dish and thin crust. It is very
much focaccia bread, if you’ve ever had that. Oh, and the best part is
that you buy it by the slice."


So, to answer your question HeartofGlass, there are 17 or 18
regional styles happening in the U.S. alone. That's before you go
global. Or before you go into "chain-style pizza," which who knows.

Updates

Source Here.

The following have been added to this list after getting feedback from the comments below.

New England Greek–Style



I had either never heard of this one or had heard of it at one point
and pushed it to the back of my mind because I rarely visit New
England, but K2kid commented about its absence in the original version of this list. Luckily, Serafina chimes in with some hallmarks of the style:

• Thin crust with a firm, but not crackerlike, bottom, which is often oily enough to saturate the pizza box
  
• Tomato sauce heavily spiced with oregano
  
• Thin layer of cheese, sometimes a blend of mozz and cheddar
  
• Cooked
  long enough for the cheese to become molten, slippery, and sometimes
  separate, coating the entire top of the pie with orange oil
  

And one side note, you can also tell you're in a Greek pizza place
by the all-Greek decor, gyro offerings, and a Greek salad that's 85%
feta cheese. Oppa!

And MikeNYC says:

This type of Greek is not to be confused with "Greek"
pizzas with olives, feta and other Greek ingredients. The dough is
pressed out into olive-oiled pans with a small rim. The dough is
pressed flat and then sauced. The pans are left out to rise, but only a
little. We would then cheese them and toss them in the cooler. That
would stop the rising. You would then draw on those throughout the day.
If you ran out, no more pizza! The base cheese was a mixture of
provolone and mozzarella. If you wanted a "mozzarella" pizza, the
pizzaman would sprinkle another layer of mozz over the base and toss
the pan in the oven. Other ingredients went on top of the cheese. When
it was done the pizza was scooped out of the pan, dropped onto a flat
cardboard round and sliced, always with a long flat curved blade that
pressed into the pizza and sliced as the blade rocked on its curved
edge. I never saw roller cutters and I'm not sure they would work as
well on the slightly thicker, crisper pies. Best things about this
style: The crust gets very firm and crunchy due to the olive oil in the
pan. It's a little thicker than NY style, but because it's risen it
seems a little lighter. That crisper crust would support the extra
cheesy "Mozzarella" pizza, and rarely got soggy.

Washington D.C. Jumbo Slice



While this one sounds like it's merely a style based on size, I've seen arguments for it in the comments (here and here) and over on Boing Boing.

While I'm not sure it's going to be a widely recognized style, It's
in the interest of Slice readers to know about it, even if it, so ...

Yes, the jumbo slice of D.C. is mainly known for its
size. There are many competing places offering this style. The link to
the article below tells about the development of the jumbo slice, the
competing claims of who has the "First Oldest Original Jumbo Slice," a
laboratory-based nutritional analysis, and the fact that people only
eat it when they are drunk. Jumbo Slice Lore of D.C. [Washington City Paper]