hah I'll try to avoid any that have already been linked, but I do read quite a few..
http://www.penny-arcade.com (Kings of the Internet. How has no one else called this yet?) *okay while I was making this someone got there first

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http://www.reallifecomics.com (office comic + imaginary troll)
http://www.mitchclem.com/mystupidlife/ (can't remember, he's had a few I think)
http://www.threepanelsoul.com/ (guys from Mac hall if anyone read that..)
http://angryflower.com/ (probably my favourite. ever.)
http://www.amazingsuperpowers.com/home.htm (deliciously random)
http://joeandmonkey.com/ (pretty much dead now, but the archives are worth a look)
http://boasas.com/ (social commentary from a head on a stick ^^)
http://e-merl.com/ (moar random!)
http://whiteninjacomics.com/comics.shtml (white ninja, nuff said)
http://www.realmofatland.com/ (fantasy style, if you like lfg have a look)
http://www.shortpacked.com/index.html (life in a toy store?)
http://www.savagechickens.com/ (erm chickenz)
http://smbc-comics.com/ (sweet sweeeet random - make sure to mouse over the red dot)
http://www.explosm.net/ (it's been said but I'll link anyway - they really push the envelope)
http://pbfcomics.com/ ('nother dead'un, but great great archives)
http://www.duelinganalogs.com/ (pretty much pure gamer)
http://www.toothpastefordinner.com/ (single panel random)
http://gucomics.com/ (almost daily updated gamer comedy)
http://vgcats.com/ (more gamez)
http://comic.truenuff.com/ (dead but hilarious, a must read archive)
erm, that'll probably do for now ;p
oops almost forgot http://www.alessonislearned.com/ just incredible.