If you live in an area with lots of wildlife and would like to get photos without having your camera constantly at the ready, you can repurpose a cheap camera, air freshener, and a microprocessor into a motion-detecting camera.
What's neat about this hack is that it's not only remarkably cheap (around $US20), but the instructions are so well laid out that anyone can do it. It definitely involves some work with electronics, but as long as you've learned how to solder, the instructions are super easy to follow. The sensor can pick up movement from 15-20 feet away and can snap a picture as long as the movement isn't too subtle—luckily, the guide has a great FAQ on using the final product too. If you're looking to get a bit more into electronics, this is probably a great project to start with. Hit the link to check it out.
Cheap Motion Detection Wildlife Camera [Instructables]