Dresden Codak
Already reviewed on the Fight.

copper
Excellent and renowned webcomic, this thing is just beautiful. Comes out infrequently.

The Order of the Stick
A comic about a rpg-style campaign in a huge fantasy world populated by stick figures. I never know what's going on but some of it's damn funny.

Gunnerkrigg Court - By Tom siddell
An atmospheric and moody comic set in a strange school. Like Harry Potter but fucked up cool.

Dicebox: Illustrated Feed
Nice art, another incomprehensible story.