What do you get when you combine old 35mm slides, a speedlight, a lens, and the genius of the DIYPhotography hackers? You get the brand new Light Blaster: a strobe-based image projector that lets you transform your photos in a flash.
By inserting a 35mm slide into the Blaster and synching it up to your camera it'll project the slide's image wherever you direct it when you release your shutter. You can create textured backgrounds, send secret messages, or give people wings!
You'll need to provide a strobe (any commercial speedlight will do) and a lens to get things working, but if you don't have any old 35mm slides kicking around, or no way easy way of printing any yourself, the Light Blaster team has put together four collections of slides: backdrops, effects, wings, and a totally random selection. When they say totally random, they really do mean it. You have no idea what might turn up in that box.
As for the lens requirement, the Light Blaster is compatible with any EF or EF-S Canon lens out of the box. Only have Nikon lenses to hand? There's an adapter for those. By changing the lens attached to your Blaster, you can alter the expanse of your projection: shorter focal lengths create wider projections, longer focal lengths project your image into a more compact area.
After that, it's all down to your imagination! (Or you can check out what other people have been doing with it, for some inspiration.)
A Canon-mount Light Blaster costs $99; with a Nikon adapter, it's $116. A box of slides is $17. You can learn more and pick up yours from the Light Blaster website.