Bunny (www.frozenreality.co.uk/comic/bunny)
Very funny web comic about cute bunnies.
xkcd (xkcd.com)
"A webcomic of romance, sarcasm, math, and language." A great web comic for people who are mathmatically inclined.
VG Cats (www.vgcats.com)
For people who live and breath computer games.
Penny Arcade (www.penny-arcade.com)
One of first, and most popular web comics. Basically only understandable to geeks and gamers who are up on the latest games and news.
Questionable Content (www.questionablecontent.net)
Nice general audience web comic that I enjoy reading. Longer, more intracate storylines than your typical comic.
Cyanide and Happiness (www.explosm.net/comics)
A very very odd webcomic that can sometimes be borderline offensive...