Casio EX-F1 time lapse kit
A 555timer with variable on time (so the camera catches the trigger) and variable off time (between photos) from 1 to 5 seconds.
I put a female 3.5mm jack onto the stock cord end of the remote trigger then put a male jack on my new trigger and the stock trigger so either can be used. The switch controls the "half press shutter" to enable auto focus.
Check out this page for more detailed info on how to hack up your own external shutter button.