This list is currently short, but I'm just getting started.
Jackson Pollock- Enough said.
Marcie Paper- Quite possibly my favorite contemporary painter. If you don't know who she is, then wise up!
Vincent van Gogh- The unoffical posterboy for emotional disturbered artists but you got to love him.
Andy Warhol- The man, the myth, the Legend! See his work here.
Andy Goldsworthy- Can you say "Inspirational." It is amazing what this guy can do with all natural materials. See for yourself.
Richard Diebenkorn- This guy KNOWS how to use color. Check him out at ArtNet
Karoly Grosz- The most amazing movie poster artist of all time. Frankenstein (1931), Dracula (1931), The Invisible Man (1933), The Mummy (1933), and Bride of Frankenstein (1935).