I realise I have quite a list of webcomics that I regularly read, so - here is a list!
http://theoatmeal.com (The Oatmeal)
http://basicinstructions.net/ (Basic Instructions)
http://www.commissionedcomic.com/ (Commisioned Comic)
http://www.cad-comic.com/ (Ctrl Alt delete)
http://www.explosm.net/ (Cyanide & Happiness)
http://www.myextralife.com/ (Extra life comics - Scott Johnson)
http://hyperboleandahalf.blogspot.com/ (Hyperbole and a half)
http://www.reallifecomics.com/ (Real Life Comics - long running :) )
http://xkcd.com/ (Sure this needs no introduction!)
Enjoy!
