Vimeo member Weelian Soh creates a simple trigger from a universal Infrared remote for Canon DSLRs. If you're familiar with Canon's video mode, so far it can only be started / stopped remotely via infrared. The trick here is to use a fiber optic cable that bends the light to the DSLR receiver. In the video (above) he uses a fiber optic cable, but a better method would be to use a shielded Optical Audio cable which you can find for 0.99 cents shipped. The actual remote being used is one you can find for under $4.00 dollars shipped. So for under $5 dollars, you can setup a pretty simple remote trigger to start and stop video mode on that Canon DSLR. [Thanks Weelian]
This is a very old technique that started by using a very slim OEM Canon RC remote which only has one button, as seen in the video below by Vimeo member Lucasberg. The video shows use of the RC1 for Canon 5D Mark II which has now been replaced by the RC6 (still one button). The RC6 is said to support a bunch of different cameras from the 5D Mark II down to simple point and shoot cameras.