xkcd is "A webcomic of romance, sarcasm, math, and language."
If that doesn't interest you, then I'm not sure I can convince you.
Here's a few favourites of mine:
Merlin (Merlin lived backwards)
Science (It works, bitches)
Su Doku (Finally one I can do)
Pong (It's what the matrix sequels should have been)
Pi Equals (This joke for Stan)
Useless (Romance + Math = ?)
If you hover your mouse over the comic you get more information.
Update: Dozy, forgot the genius Comic Fragment.