“The Watchmen”
With honourable mentions to :
[ul]
[li]“V for Vendetta”[/li][li]“The Dark Knight Returns”[/li][/ul]
Whats yours?
I’ve only got one word: Preacher!
Akira
Agreed, except the Preacher is a comic book series. 
Frank Miller’s Give Me Liberty
The Watchmen
Kingdom Come (The fight between Superman and Captain Marvel freakin’ rocks, and the artwork is truly art)
Batman: The Dark Knight Returns by Miller
Ronin by (You guessed it) Miller. This is the best graphic novel of all time, IMHO.
I’ve just finished Gone to Texas and it’s very , very good but I’ve been told it goes downhill after that .
I am going with The Watchmen as well!
Frank Miller’s 300
Both Sin City an the various Usagi Yojimbo GNs are worth mentioning.
As is Dominion: Tank Police.
Joke! (I wouldn’t want anybody to shoot kryptonite arrows at me.)
I liked Watchmen, but I wish it had ended differently. The thing about that novel that was so intense was, I liked some characters a lot, and some I wish were just never there.
Dr. Manhattan: Too powerful for the universe, although at least this was dealt with in an interesting way. (“I have universes to create” was his last line? Or “I have worlds to create”?) I kind of thought it was neat that he would assume multiple forms sometimes while romantically occupied.
Ozymandias: Rich heroic dude with lots of neat plans and technology … I’ve seen this one too many times. I liked his name, but that’s about all that really grabbed me.
The gang of non-super heroes: The “costumed vigilantes” backstory was wonderful. What causes some ordinary person to dress up in tights and beat up street criminals in the middle of the night? Any number of things! There all here! I liked Nite Owl, Silk Spectre (spelling?), and especially Rorschach. sniffs sadly
I think my favorite one so far was Why I Hate Saturn. People always describe it the same way, “Yeah, it’s like a superhero comic, but it doesn’t have any superheroes in it. Well, there’s one, but she’s not a big part of the plot. Well, she’s a big part of the plot, but the plot’s not a big part of the book…” Lots of fun. My favorite dialogue, taking place in an airport (bus station?) full of coin-operated televisions, paraphrased: “Hey lady, can you spare a quarter?” “No way, I know you’re just gonna use it to watch TV.” “No, I was gonna spend it on liquor. Honest!”
I prefer V for Vendetta to The Watchmen, but both are good.
Appleseed is excellent. (Shirow is great.)
And of course, the Sandman collections are also great.
While there are some excellent choices so far, the best is indisputable:
Maus (and Maus II, since their one single story).
On importance and subject matter, it wins hands down.
I’m kind of disappointed by you guys actually, it took that long for The Sandman</i> to appear?
Goodness, it easily beats out any of the other competitors so far.
The greatest? I don’t know but here’s a list of several I’ve found worth reading more than once:
The American
American Flagg
Astro City
Aztec Ace
Big Black Kiss
Books of Magic
Buck Godot (and XXXenophile and everything else by Phil Foglio)
A Cartoon History of the Universe
Cerebus (all of them)
Changes (and everything else by Matt Howarth)
Concrete
The Cowboy Wally Show (and everything else by Kyle Barker)
The Dark Knight Returns
The Elementals
The Golden Age
Jon Sable, Freelance
Kingdom Come
Love & Rockets (all of them)
Omaha
Preacher
Sandman
The Spirit
The Watchmen
And undoubtedly several more I can’t recall at the moment.
I’ll concede Sealemon’s point that several of these might not qualify as graphic novels. But they’ve all got words and pictures, they’re all available in book format, and they’re all good.
You damn kids! {shaking fist from vantage point in the ol’ rocking chair}
No one has ever topped Justin Green’s BINKY BROWN MEETS THE HOLY VIRGIN MARY.
Yeah, okay, call it a “comic book.” That’s because they didn’t HAVE oversized paperbound graphic novels in 1973. (it has since been collected along with all the other Binky Brown material into an actual oversized paperbound graphic novel.)
I also spent the greater part of the 1980s marveling at the Hernandez Bros’ LOVE AND ROCKETS. Does that count as a comic book series or a serial graphic novel?
Myth Adventures one and two. From Robert Asprin’s novel. Illustrated by Phil Foglio. Absolutely wonderful. Not only are the writer and artist made for each other, my old copies (I think they’re about 15 years old) have held up under multiple readings. Phil did the illustrations in the old Starblaze printings of Asprin’s work, and he was great with them.
Lynn and Little Nemo, Yes, Phil Foglio does excellent work, I treasure my copies of Stanley and his Monster, Buck Godot (I must read PSmIth about once every two months.), and of course my What’s New![sub]With Phil and Dixie[/sub]. But I’m not sure they really qualify as greatest.
Buck Godot, Watchmen, and Sandman. I like to say “Watchmen
was aterrible comic book & a great graphic novel”.
There are a couple of titles I haven’t even heard of mentioned so I’ll go look for them when I get paid or of course I could just stand in the shop and read them . 
Thx guys/dolls
I can’t believe no one here has mentioned the STARMAN collections. There’s by the same writer as the Golden Age (which someone did mention) and the artwork is as amazing as the story. It presents family relationships in a way that really hits the reader in the heart.
I can’t believe that no one has mentioned ElfQuest yet?!?!
ElfQuest is obviously the best!