asmodaus:
You can never go wrong with Frank miller's Sin city.Unless you have an unnatural phobia of blood and gore, in which case stay away. STAY FAR AWAY!

Seeing as how he obviously enjoyed Wanted then I don't think that's going to be a problem.

The Dark Knight Returns-Frank Miller

Trigun (manga)-Yasuhiro Nightow

Anything by Alan Moore

Crimson was pretty decent, nice take on a vampire story. It's divided into four volumes and unfortunately has a bit of the Indigo Prophecy syndrome about it towards the end. Nothing too terribly bad, it makes a bit of sense as to why it goes where it does, but still.

There's another one by Marvel. Origins, I believe the name is. It's basically Wolverine's whole backstory, or rather, how he found out he was a mutant and what kind of person he was before.

Fables is another great one, has that whole 'fractured fairytale' feel to it.

Emperor Joker was another good one, well, what I got to read of it anyway. Pretty nice if you're a DC fan.

I Am Legend is supposedly pretty good, only got to read a few pages, and what I read was good so...yeah.

The League of Exrtaordinary Gentlemen is pretty good. As for manga, give Battle Royale, Death Note and Akira a try.

Thanks, Paleboy.
Looks like everyone here are recommending very gritty stuff. I'm really not an expert at that genre, but if you don't mind delving into manga, then you can always try out series like Berserk. HunterXHunter might look innocent enough, but will probably be to your liking as well.

Preacher is really good. It can get seriously messed up at times, though.

Well, since the League of Extraordinary Gentlemen has been mentioned about seven thousand times, I think I am implored to read it.

Recently a book came out called "500 Essential Graphic Novels". Title pretty much says it all. In the mean time, I'll try to think of a few the others have missed.

Batman: Hush is great. The same guy who wrote The Long Halloween did it, which is appropriate seeing as how they're both perhaps the best Batman comics ever (don't make me choose).

Bone: the full volume black-n-white edition is already available, or you can wait for a few months when scholastic finishes releasing the full color volumes (the first 8 are already out, if you want to get started).

Somebody already mentioned Cerebus and Y: The Last Man, both excellent. Cerebus is a bit on the pricy side, though, and only full fledged comic stores will carry it (no Barnes-n-Noble or Borders that I know of carry it), whereas Y is cheap and abundant. My advice: buy the latter now, ask for the former for Christmas (that's what I did).

Anything by Allen Moore or Frank Miller is pretty much a given. Neil Gaiman too (Sandman, Mr. Punch, ect.)

As for manga, assuming you're secure in your masculinity, Love Hina's pretty good (actually, given the amount of fanservice in it, there's probably no risk of emasculation from reading it). Death Note's another classic, with Shojen Advanced as affordable as ever (a good 2-3 dollars cheaper than other manga publishers). For more light hearted fare, the works of Kiyohiko Azuma (Azumanga Daioh, Yotsuba&!) are a must.

And that about does it for now. I'll write back if I think of any more.

Like most people have said:

Watchmen
Y: The Last Man
V for Vendetta

Also, from what I've read of The Dark Tower graphic novel it is pretty good.

Is there something wrong with the words "comic book" now? I've never understood the need for pretentiousness that drives "graphic novelists". Dr. Seuss was a graphic novelist. The whole thing makes me think of illiterates who need pictures in their books.

SimuLord:
Is there something wrong with the words "comic book" now? I've never understood the need for pretentiousness that drives "graphic novelists". Dr. Seuss was a graphic novelist. The whole thing makes me think of illiterates who need pictures in their books.

The way I look at it, "comic book" describes the small, 20 pages long or so, books, and "graphic novel" is for the larger, 100+ page books (usually a collection of several of the smaller comic books). Terms for size, rather than content.

Anarchemitis:
Well, since the League of Extraordinary Gentlemen has been mentioned about seven thousand times, I think I am implored to read it.

Good. It's fantastic.

If you're like me and find the idea of superheroes who wear their underwear on the outside ludicrously idiotic and cretinous (I'm looking at pretty much every American superhero comic ever produced), then I'd wholeheartedly recommend "Marshal Law," a brutal satire on the superhero genre of comics and imperialist America written by Pat Mills and drawn by Kevin O'Neil (The same artist of "League of Extraordinary Gentlemen.") I think Garth Ennis came up with the idea for "The Boys" after reading this gem. In fact, I'd recommend almost everything written by Pat Mills if you have a penchant for political satire, such as "Charley's War," "Nemesis, the Warlock,"(Also drawn by Kevin O'Neil) and "Requiem Chevalier Vampire."

The Franco-Belgian comic scene has tons of cerebral and subversive comics, like the "Nikopol" trilogy created by Enki Bilal and "XIII" created by William Vance and Jean Van Hamme. The magazine "Heavy Metal," which was the offspring of the great French magazine, "Metal Hurlant," features lots of great underground comics.

As for American comics, I think most of them are complete shit. However, in fairness, I did quite like "Kabuki" and "The Red Star."

ThaBenMan:

SimuLord:
Is there something wrong with the words "comic book" now? I've never understood the need for pretentiousness that drives "graphic novelists". Dr. Seuss was a graphic novelist. The whole thing makes me think of illiterates who need pictures in their books.

The way I look at it, "comic book" describes the small, 20 pages long or so, books, and "graphic novel" is for the larger, 100+ page books (usually a collection of several of the smaller comic books). Terms for size, rather than content.

Once again, when you say "comic book", people think "Oh, for children!"
It's sort of an attempt to kill the myth that comics are only for kids. Or at least differentiate between kids' and adults' comics (and trust me, a lot of the stuff mentioned is not for kids!)

Anarchemitis:

MAUS by Art Speigelman

It took me about 3 sittings on the toilet to finish that one. Was an interesting read. I'd recommend it.

I think everything i like has already been mentioned, except for "Squee!" by Jhonen Vasquez.

It's a follow up to Johnny the Homicidal Maniac, centering on his neighbor, a paranoid, traumatized, yet sometimes cheery boy. Found it to be a bit funnier and less pseudo-preachy than JTHM. And it's extremely mean.

Ooh yeah! "Marshal Law" and "Squee" are both great, and you are right, "Squee" may be one of the meanest comics I've read in a long time. Vasquez did another follow-up to JTHM and Squee, called "I Feel Sick." It's very good, very typical Vasquez, and after I loaned it to a friend, it lead to us throwing the following exchange randomly into conversation:

"I'm going to rape you up the butt and throw you out the window!"
"Whyyyyyyyyy....?"

A_Red_Sky_Morning:
The Sandman, written by Neil Gaiman; I've heard promising things about it.

Hope this helps.

Having read them, i absolutely love them. But they may not suit your action orientated requirements thus i suggest:-
-The old rogue trooper collections from 2000AD
-The dark knight some and i stress only some of DC's darkhorse batman is awesome
-The original Akira sequence
-Apparently someone has just done a cool looking graphic telling of the Musashi legend, and that is a sweet and action filled adventure
http://www.boingboing.net/2008/09/02/manga-illustrations.html

-Maus 1&2 by art Speiglman are is an incredible story, phenominal.

-and if your only just getting into graphic novels, this is one of the seminal works about the subject in true style

http://www.amazon.com/Understanding-Comics-Invisible-Scott-McCloud/dp/006097625X/ref=pd_sim_b_5

Mhm, agree with Rogue Trooper. And like to add in the Judge Dredd Complete Case Files series, that is each book is a collection of progs/stories that the man himself has starred in. Dialogue is a little corny at times, but it's good stuff.

Another I'd recommend is Slaine, it's kind of a twisting of Irish/Celtic/Norse/Old English history. But above that, give the Book of Invasions series a try too, it mixes art, photography and photoshop magic that comes out as something freaking awesome looking :D

As for the comics versus graphic novels debate. I too always considered it more of a format thing, i.e. Comics refer to the soft paper-back individual issues, and a graphic novel referring to either the collected content of such issues, or fully contained stories in their own right bound with card. Although I do realise that some people do talk down at Comics as being for kids, but if you're into them, it shouldn't really matter what anyone else says about it. Although I can sort of understand someone saying they only read graphic novels over comics in an effort to get away from that notion. Kinda stupid yeah, but, not much you can do about it.

The Preacher series is pretty good.

Also try sandman, neil gaiman is amazing

Frybird:
I think everything i like has already been mentioned, except for "Squee!" by Jhonen Vasquez.

It's a follow up to Johnny the Homicidal Maniac, centering on his neighbor, a paranoid, traumatized, yet sometimes cheery boy. Found it to be a bit funnier and less pseudo-preachy than JTHM. And it's extremely mean.

That's the exact same way I feel about JTHM and Squee, couldn't have said it better.

Death Note and Battle Royale.

Both are really well written. The characterisation is wonderful and the stories are gripping, not to mention seriously thought provoking.

The Hedge Knight is another good one. It's based on a novella that takes place in the same setting as A Song of Ice and Fire by George R.R. Martin (so you could just read the novella if you'd rather). It's about a young man who takes part in a jousting tournament, hoping to become a true knight. Sort of like that movie A Knight's Tale, except, y'know, not shitty.

Dusk, and Dawn - by Tim Lebbon

Other books by Mark Millar: Chosen, as well as Superman: Red Son.

I kinda like that one Halo graphic novel with the story about New Mombasa before it was invaded. Plus it had a graphic novel on how Sgt. Johnson escaped the flood, which I thought was pretty badass....Well I thought it was. But thankfully it's not the Halo games turned straight into a graphic novel, but instead stories about other characters

mshcherbatskaya:
Ooh yeah! "Marshal Law" and "Squee" are both great, and you are right, "Squee" may be one of the meanest comics I've read in a long time. Vasquez did another follow-up to JTHM and Squee, called "I Feel Sick." It's very good, very typical Vasquez, and after I loaned it to a friend, it lead to us throwing the following exchange randomly into conversation:

"I'm going to rape you up the butt and throw you out the window!"
"Whyyyyyyyyy....?"

Damn, as if my "to get" list wasn't long enough, I've got one more to add.
Ok, one of only 2 Superman's I'd ever recommend (Red Son has been mentioned already. Oh, and I usually Hate Superman): Superman: True Brit. John Cleese helped write it, that should be all you need to know.

I personally love Dragonball Z manga. I never had nay before, but you can get 3 volumes in one book now, making them feel a lot more substantial. Even so, they are not to everyone's tastes.