My aunt has a Canon Rebel XTi. In an effort to help eliminate camera shake, I decided to try to build her a remote for her camera. Fortunately, the XTi has a pretty simple remote control interface. It is basically a stereo 3/32 (smaller one) headphone jack connected to some buttons. To be honest I wish my Nikon D90's interface was as simple, but I digress.
I searched the web and I found very simple instructions here:
I bought a couple of push buttons at radio shack. I used a Goo Gone bottle as the housing. The wires were left over from other projects, I tried to use a jack from a cell phone headphone/microphone head piece. However the jack was designed to carry 4 signals instead of a regular stereo jack which carries three. As a result, the cell phone jack didn't line up in the body of the XTi as it should. I may have been able to get it to work with a little more effort, but it was more simple to just go find a stereo jack.
Here it is. It works, and isn't flashy but hey. I think it would look cool to put a bunch of L.E.D. lights in there, but...
As an aside: My soldering sucks. You would think that after all the "do it yourself" projects I have tried to do, I would start to get better. But no... I may be worse than when I started.