Machinima, defined by Wikipedia, is "a collection of associated production techniques whereby computer-generated imagery is rendered using real-time, interactive 3D engines, such as those of games."
Um, okay. All Games Radar knows is that watching one Master Chief kiss another Master Chief is funny as hell. So are two SPARTANs arguing over the morality of teabagging, or an Elite ordering food at the drive-thru. A skilled machinima director can make you laugh, cry, feel fear... completely within the confines of the game's environment.
Before announcing Games Radar's favorite Halo 3 filmmakers, here are the rules. First, the machinima had to be Halo 3 (so no classic "Red vs Blue"). Second, the clip had to be in-engine, not stuff with action figures (so no "Arby 'n the Chief" or "Master Chief Sucks at Halo"). Now, the envelopes please.