Oh god, so many different ones I love - V for Vendetta, League of Extraordinary Gentlemen, Sandman, Action Philosophers, Ghost World, Fantastic Four, the Flash, JSA, Starman, Green Lantern Corps, Tank Girl, 2000AD, Nextwave, and there's so many more on my to-buy list. Really want to get my hands on DC: The New Frontier, I've heard it's great.
Superhero-wise, I usually go for what I've heard is well-written rather than specific characters, but there's a few exceptions. I'll read absolutely anything with the Golden Age Flash in. C'mon, supersonic pensioner in a stylish hat, what's not to love?