Cyanide and Happiness is one of my favorites, however XKCD takes the cake by far. You have to be a sort of science/math/programming nerd for a lot of the jokes though
Saturday Morning Breakfast Cereal is one I've picked up recently, which I like a lot, and Perry Bible Fellowship was another good one, but it stopped updating ages ago afaik.
I read Sequential Art, it's pretty good, and Sinfest, which is another one of my top favorites. Rogue Robot I used to read, just because an old friend of mine is the artist for it, but he got busy with other stuff and the production of the comic came to pretty much a halt. On the occasion I'll read the Rooster Teeth comics, but they aren't all that funny, really.
I'm not a fan of CAD personally. I don't know why. I guess I never picked up on the extreme gamer humor or whatever. VGcats I've liked now and then, but I don't monitor it for updates.
From what I've seen, Looking For Group is really good, but again, I've been too lazy to monitor the updates on that one
--donut3.5--