I finished 8 Bit Theater sometime in high school. It was one of those webcomics that actually has an ending. After that, I discovered XKCD, which is more of a math/science/computer nerd webcomic. I don't get all of their jokes, but the ones that I do get are hilarious. And the hover-text is almost always as funny as the comic itself.
Abstruse Goose is sometimes similar to XKCD, but sometimes it is more like Cyanide and Happiness.
I love Cyanide and Happiness, which is filled with dark humor.
I rarely read Buttersafe and Doghouse Diaries, but they are also both hilarious.
I just discovered Feel Afraid. It is mostly silly, with some occasional dark humor.
Subnormality is more of a social commentary that is occasionally funny. It is also very text-heavy. I definitely have to be in order to want to read it, so I don't read it very often. Unlike many of the other webcomics I read, this one kind of has a storyline. It is sometimes about a sphinx trying to live in the city.
Those are all of the webcomics I read right now, so that's it.