I could put descriptions next to comic names, but well, here's the bottom line: there're all great comics. You should really visit all of them when they respectively update. That's basically what I'd say about all of them in more specific descriptions anyway...
 

COMICS:

8-Bit Theater
Adventurers!
Avalon
Beta the Strip
Demons in the Background
The Jar
Kai-chan in Tokyo
Kung Fool!
Luminosity Pro
Luna's Moon
MacHall
Maison Otaku
MegaTokyo
Okashina Okashi
Otaku Comics
Penny Arcade

COMICS (con't):

Ryo's super cool site
Real Life
RPGWorld
Self Insert
Stubble Comics
Thieves
Toast in the Shower
Under Power
Wolfe's Den

ETC:

Dragon Magic Online Store buy anime and more
Neko Neko Wai! Release your inner neko.
Revelia Castle 1/2 comic 1/2 etc.. hmm..
Aniverse.net Check out #MegaTokyo on irc.aniverse.net
Angerdog Studios Angerdog's art, check it out