Intervalometer
This was a very quick project I did to explore time lapse photography. An intervalometer basically sends out signals to a camera to tell it to take a picture at a repeated interval. Mine is currently set to take a picture every 30 seconds. I just used an Arduino library I found that did all the work for me. I had to write maybe a line or two of code, and the circuit is dead simple, an IR led, resistor, and a wire. I recovered the IR LED from a TV remote that had lost its TV. One of the coolest parts of this is that I don’t have to modify the camera in any way, the Arduino just emulates a Nikon remote. The camera is also completely electrically isolated from the Arduino, so if I messed up at all, there is no risk at all to the camera.
I set the camera up to do a time lapse of my backyard, but I have no way to power the camera other than a battery, so it doesn’t work so well. I’ll upload a video here once I’m done editing it.
Here’s a couple pictures:
Camera and Arduino set up
Arduino and the circuit.
adcurtin 
Have you thought about trying to hack a power supply for the camera? It would be cool if you could keep it plugged in and running for a long time.
I’ve thought about it, but the camera isn’t mine, and it’s like $800. It’s also a nonstandard battery, and like 7.2v (so I don’t really have a power supply). If it had a power input jack or something, I’d try it out (or if I could buy one for like $20 or so). But with how it is now, there’s no chance that I’d even try something like that.a I found that if I pay attention, and use 30 seconds for each shot, I can charge a spare battery and swap it out between shots. Not a good long term solution, but if I want to shoot for a day, it works out. I might look at using a different camera (webcam?) that would be easily powered externally, but wouldn’t take as high quality of shots.