DIY: Make a Disposable Camera Your Slave Flash
It's tough to shell out cash for a new flash unit, but you don't always have to buy new. Instructables member Wired Cur has developed a way to use an old disposable camera as a flash slave.
The nice thing about this particular project, in addition to its usefulness and inexpensiveness, is that the main component is something that's just going to be thrown out anyway. Most photo processing places will have disposable cameras just lying around waiting for the garbage or recycling, and it shouldn't be too hard to convince an employee to give you their trash.
It's a bit of a complicated process, and of course, you need to make sure you have a disposable camera with a working flash. You'll need a wireless flash trigger, a drill, some pliers a utility knife and a soldering iron, along with some basic knowledge of soldering.
Once you're done, you'll have a nice controllable slave flash, and you can even link up multiple flash units if you like. The full instructions and detailed pictures of the setup are available at Instructables.