Fun With Flashes
This is a filter and gel sample book that you can get for free from most stores that sell film expendables.
The book holds small 3 inch samples of different gels. On top of being a handy tool to figure out what kind of lighting you want for your movies... It's just the right size to cover a camera flash on your SLR.
You can use it as the primary source of light for a really extreme look (fun for parties... or your cat, if you are lame and have no parties to shoot at the moment):
Or as a seconday source to play with a splash of color, or even to give you some weird colors in your shadows:
I either hold the book up to the flash, cut out the sample and tape it, or you can put it inside a homemade flash diffuser.