Open Source Filmmaker, a community bringing together some of Steam's best movie creators, recently held a themed event called "Turret Week". Members had to create short, original films about Portal's turrets.
While most Source Filmmaker clips are still rough, unoriginal affairs using Team Fortress 2 models, these are wonderful, capitalising on the short timeframe and source material to produce some great results.
You can watch all 22 at the playlist below, which you really should, as many contain running gags.
Turret Week [SFM]