Boy on a Stick and Slither - surreal humor. It's dead now, and judging by my friends is a minority taste, but has several of my favorite strips to its name. http://archive.boasas.com/?c=286
Sam and Fuzzy - Hard to describe. The cartoonist does a great job making sure there's a joke in every strip, despite involved continuity. http://www.samandfuzzy.com/1482
Piled Higher and Deeper - grad students. http://phdcomics.com/comics/archive.php?comicid=591
Extra Ordinary - surreal humor. http://www.exocomics.com/05
Boy on a Stick and Slither - surreal humor. It's dead now, and judging by my friends is a minority taste, but has several of my favorite strips to its name. http://archive.boasas.com/?c=286
minus - more surreal humor. Also dead, but excellent. http://www.kiwisbybeat.com/minus13.html
Jesus and Mo - making fun of religion and the stupid things it inspires people to say. http://www.jesusandmo.net/2006/05/11/skin/
Sam and Fuzzy - Hard to describe. The cartoonist does a great job making sure there's a joke in every strip, despite involved continuity. http://www.samandfuzzy.com/1482
Station V3 - originally great. Hit such an awful dry spell that I unsubscribed, but hey, maybe it's funny again. http://www.stationv3.com/d/20110722.html
Of those already listed, I also endorse savage chickens, xkcd, basic instructions, and sinfest.
http://xkcd.com/349/
http://www.savagechickens.com/2010/11/identification.html
http://basicinstructions.net/basic-instructions/2010/1/10/ho...
http://sinfest.net/archive_page.php?comicID=4746