My favourite webcomic currently is, and will likely remain, the Order of the Stick. In a world based on Dungeons and Dragons, you get an interesting plot and compelling characters. You do not necessarily need to be an expert of the game; a basic knowledge is enough, and even then the humour is not solely based on D&D jokes, far from it.

I like Kevin & Kell too, I would list it as my second favourite. Updates everyday.