Intro: Wireless Arduino Remote Camera Trigger
Wired camera triggers typically work by acting as a switch. Camera circuitry operates at 3.7V (a single Li-Ion cell, i think) so you can either complete a physical switch to trigger the camera shutter, or you can apply 3.7 volts across the two contacts to trick the camera into firing. In this project, I used an Arduino to apply the 3.7V to activate the camera trigger through my old mouse camera trigger.
The Arduino Fio was controlled over XBee radio modules (efffective range of 250 feet...? ish...). I wrote a simple program on my laptop so that when i clicked in a window, it sent a command to briefly apply voltage to an I/O pin on the Arduino. It could also be automated, so that the Arduino is an intervalometer.