Seriously, the best webcomic of all time.
It's currently running its fourth story (or "adventure"). The first two were kinda eh, but the third one (Problem Sleuth) was damn awesome. It was basically about a private detective who couldn't find a way to leave his office. Whereas this sounds like it's a cliché, it turns into this huge, complicated story involving... ohgod, too many people and things. It's awesome. It's like this silly story that the author let go WAY THE FUCK out of hand. How out of hand? The worst you can imagine, and then some. For reals.
But that's basically all of MSPA.
The current adventure, called Homestuck, is still going on, with regular (multiple pages per day, usually) updates. It's about four kids playing this game. A game that's summoned a whole bunch of huge freaking meteors to earth. The real earth. Not the game version of earth.