Dark Knight Returns (Frank Miller) is prolly the best graphic novel I’ve read. Batman Year 1 (Miller again) is well up there too.
Batman Hush has outstanding artwork from Jim Lee (Batman just looks ‘right’)and the story is pretty good as well.
1602 (Neil Gaiman) is a good read, though it helps if you know somthing about the Marvel characters in it first
Arkham Asylum (Grant Morrison) is very good, but very very dark
If you can get hold of any of the Joss Whedon (he of Buffy and Firefly fame) written X-Men, they are well worth a read.
League of Extraordinary gentlemen Vols 1 & 2 (Alan Moore) are brilliantly clever in their use of famous fictional characters, but later vols are just on another freaky-deaky planet.
V for Vendetta, Watchmen and From Hell (all by Alan Moore) are all worth a read as well
I’d suggest you go down the Library as well – my local (Taunton) has a fantastic stock of graphic novels.
Hmmm I think I may need to get out more…
Toby