A friend of mine recently turned me on to the webcomic "Order of the Stick", (you can read it from the start here).  It's quite a funny take on table top gaming, and I've been steadily reading through them, quite often laughing out loud.  Good stuff.  It is amazing how much meta-humor content there is out there relating to games, especially the various MMOs like World of Warcraft.  Of course, not all that much of it is good, which is what makes OOTS quite remarkable.

I don't think it's as popular now but I definitely remember a time where "Agetoons" were popular among the fan community, especially at Age of Empires Heaven.  Basically humorous screenshots (usually hand created with the editor), photoshopped in to make a joke.  As Sturgeon's Law dictates, most of it was crap.  But there were a few humorous ones, and it always struck me as interesting the way our game content would be repurposed in such a fashion.  Nowadays I listen to mashups on the radio and see photoshop every night on the Daily Show, so it's hardly unique... but still interesting to see.  In fact, I suppose one could make the argument that exploring a game universe in a new direction like Halo Wars is the same basic concept...