The Gary Fong™ Origami Diffuser Thingy (patent pending), while not too terribly impressive at diffusing light, does come with a Gary Fong™ Rubber Band Thingy (all rights reserved), which can be useful. Here it's holding the S.E. Amesse Snoot Thingy, which is made of a tabbed index card and a bobby pin. My design is open source; feel free to copy.
When it comes to light-shaping tools, it's often possible to make do with a bit of imagination and some readily-available office and household supplies. As David Hobby points out on Strobist.com, there's no need to spend $100 on a piece of glorified Tupperware when a real Tupperware would do the job just as well.