I can't not also include this one -- it's a classic. (Here's the folks at Language Log debating the punchline, included because I'm a language geek.)
Dinosaur Comics is a talky, clip-art style comic addressing an eclectic range of subject matter with zany energy. Enthusiastic T-rex philosophizes while stomping things, straight man Utahraptor acts as the voice of conscience and dramatic foil, and bystander Dromiceiomimus sometimes chips in, too. It also employs the fairly cute gimmick of using the exact same sequence of panels for every strip, which must be a great timesaver if nothing else.
David Malki's Wondermark, sometimes traditionally comic, and sometimes bizarrely abstract or simply surreal, derives its success from the calculated juxtaposition of stuffy, Victorian-era illustration with biting postmodern irony.
The Perry Bible Fellowship is a collection of comics by Nicholas Gurewich, whose bright candy-colored world is severely twisted and strange. Apart from his brilliantly dark imagination, Gurewich is also a very talented illustrator.