So you want to mount your Canon Digital SLR on a tripod to get better digital pictures. Excellent - now you need a way to trip the shutter without moving the camera. You could use the camera's built-in self-timer, but your subject may be long gone until it fires. The Canon Remote Switch RS-80N3 may be the answer for you.
The Canon Remote Switch RS-80N3 is a very simple device - it simply plugs into the side of compatible (there are many) Canon EOS Digital SLR cameras. Compatible cameras include the Canon EOS 1D, 1Ds, 1DS MARK II, 1DS Mark III, 1D Mark II, 1D Mark III, 5D, 10D, 20D, 30D, 40D, D30, D60 ... Missing an N3 port, the Rebel series (4xxD) models as of this writing are not compatible. Try the Canon RC-1 Wireless Remote Release for at least most these models).
There is one button on the Canon Remote Switch RS-80N3. Like the camera's shutter release, the RS-80N3 supports a half-press or full press - which releases the shutter. In addition, the remote release button slides forward while pressed in - this will lock the shutter open in B (Bulb) mode.
Pictured above is the Canon Remote Switch RS-80N3 beside the larger, more expensive and more capable Canon Timer Remote Controller TC-80N3. The Canon Remote Switch RS-80N3 is very light but relatively expensive but valuable to own - it is a valuable piece of kit to have.