xkcd - "A webcomic of romance, sarcasm, math, and language"
Goblins - DnD Goblins start taking levels as player characters, an interesting take on good vs evil from the side of the supposedly evil side. Never played DnD in my life, but the comic's excellent. Visual style starts a bit poor but massively develops later on.
Cyanide and Happiness - Shouldn't laugh but I always do.
Phoenix Requiem - Victorian supernaturalism
Gone with the Blastwave - post-apocalyptic war spoof
Vexxarr - hugely witty, very funny. Story of an amorphous alien and his psychotic AI companions sent to conquer Earth
Menage a 3 - pretty funny, webcomic about a nerdy guy who suddenly ends up with two very sexual female flatmates
mspaint Adventures - new one's not that good IMO but the Problem Sleuth adventure's fantastic.