I would like to make a flashlight with a rechargeable prismatic lithium cell and Luxeon emitter in the smallest possible package. I want to do plastic welding with Lexan for the case, I can shape it with as little bulk as possible.

One of the big questions is how to do an on/off switch. I wanna be as waterproof as possible. The ones I'm familiar with are larger than I'd like, enough to add 50% to the size just to give it enough room. I was even considering a magnet on the outside and a magnetic reed switch inside. Even then I don't know a really good, tiny way to do the magnet so I don't think so.

Any ideas? I'm probably already going to have to add circuitry inside to regulate the power to the LED, so there may be a number of things I can try. I'm even considering a microphone where I'd just rap the device to turn it on/off.