The introductory cinema from Nintendo 64 classic Super Smash Bros. as reenacted by the cast of Team Fortress 2? Fan service doesn't get any better than this.
Crafted within Garry's Mod, a Half-Life modification that allows creative gamers to manipulate any character or object used in games based on Valve's shooter, the finished product is an almost perfect recreation of the Super Smash Bros. opening cinematic.
The music, the quick cuts, the camera angles -- everything is spot on, and obviously demonstrates a great affection for both Nintendo's game and Valve's characters.
The only issue I have is that I now badly want to play a Smash Bros.-style fighting game starring the TF2 cast. Then, of course, extrapolating on that idea makes me crave a game pitting the TF2 cast against Nintendo's characters. And inevitably I start imagining situations to explain why all this fighting is taking place.
Maybe Heavy sat on Pikachu by accident, or maybe Link stabbed the Medic to see if he was a Spy. If I was writing fan fiction, I think this is the point where Pyro would look longingly into Luigi's eyes before slowly unbuttoning his flame-retardant suit and ...