As you may be aware, Mike Nelson, head writer and one of the hosts of Mystery Science Theater 3000, has recently gotten back into the making fun of movies game with Rifftrax. Joining him on many of these tracks is Kevin "Tom Servo" Murphy and Bill "Crow T. Robot 2" Corbett (sorry for those who prefer the years with Joel and Trace).

They currently have a feature on Cuts.com where you can create your own humorous commentary track. Simply upload any clip hosted on Youtube, and select from a smallish library of recorded riffs from the gang (for those who want to write their own gags, you're going to have to settle for on screen captions).

Here's an example I just created. I'm sure someone on here can do better.