With the growing popularity of DSLRs that can shoot HD, manufacturers are jumping in with related accessory gear to solve various production needs.
Switronix's FLEX-RC1, for example, triggers HD video start and stop recording for the Canon EOS 5D/7D. That's useful when the camera is mounted on some type of frame, since the shooter can trigger the IR (infrared) on/off interface on the front of the camera by bending the lamp on its gooseneck around to the front IR window. Trying to click that switch is awkward when you're holding the camera in a support frame. Meanwhile, triggering the on/off switch with your finger can cause vibrations in the small camera body.
You could also mount the FLEX-RC1 on a mechanical arm up to 1 meter away to trigger the camera on a tripod without worrying about vibration. The unit is 2.5"x1.5"x1.5", features all metal construction, and is powered by two AAA batteries.