gels

Photographytalk has this terrific article about color correcting gels.  I just ordered the Roscolux Swatch Book, myself.  It has more colors even than the Strobist set, and although intended as a sampler, can, of course be used to color correct and it's only $4.00!

Now, though I will use these for color correcting the standard way, I also have two other purposes for these little buggers.

The first is to transform my white backdrop into a myriad of different colors.  I may even overlay patterns or pictures on gel colors that I know I won't need for any other purpose.  Just be sure to project the color or pattern on the backdrop behind the subject unless you actually want it on them, too.

The second is a cloudy day cheat.  If you are shooting people outdoors on an overcast day but would like some blue or other moody sky effects, do this:  Set your camera white balance to tungsten (this will blue-up everything).  Then put a piece of CTO (color temperature orange) or two on the flash to warm your subjects back up.  Instant awesome look.

Good luck and good shooting!  ~RW