I've always liked this set of non-animated sorting algorithm visualisations:

Shell Sort

While I have mad love for pretty much everything Alan Moore writes, I think 'Watchmen' is too firmly steeped in comic tradition to be the 'greatest' graphic novel. Amazingly influential, yes. But when large thematic portions of the story are told via a comic-within-the-comic technique (Moore loves his meta-narrative), it can be a big stumbling block to people who aren't well versed in the history of the genre (and I state this from having pushed the book on everyone I know).

Moore's 'V for Vendetta' is an equally powerful yet entirely self-contained work that I have a lot more success in recommending (or did until the film killed any interest in it with it's godawful, pointless changes). 'The League of Extraordinary Gentlemen' is a lot of fun if you have any familiarity with Victorian literature (and also totally destroyed by a godawful film). His 'Lost Girls' is an astounding work of both pornography & literature. 'Promethea' is one of the best occult primers I've ever encountered.

See? Totally smitten with the guy :)

Other more recent works that I can't recommend enough:

• Scott Pilgrim - part slacker romance, part video game pastiche, a totally new style in storytelling
• Barry Ween, Boy Genius - 'Dexter's Lab' meets 'South Park'
• Girls - one of the most original first contact stories I've ever read
• Ex Machina - Superheroes meet 'West Wing'
• Y, The Last Man - Something kills all of the males on the planet but two...

Okay, so some of those are series of trades rather than a singular graphic novel, but they all rock my world.

mouser: did you see that Larry Marder is finally releasing new 'Beanworld' material? There was a Holiday Special released just prior to Xmas, and it looks like Dark Horse is going to re-release the earlier trades as well as continue with new stuff. (I'm really surprised it's with DH given everything he's done for Image over the past decade.)