Ok, its not really solar powered, but I have found an inexpensive little gadget that can be pressed into service if you are building a DIY beauty dish. Woolworths sell a cheap solar powered garden light kit with eight lights. The lights have a platic dome with a mirrored hemisphere inside that is designed to throw light from the centre out sideways.
This can be placed in the centre of your DIY beauty dish to throw some of the light from your flash out to the sides of the dish. I used it on the 24cm gridspot I made earlier and it does help make the light more even eliminating the hotspot. If you are building a beauty dish, this could be the component you are looking for.
What do you do with the leftover bits? The seven remaining lights can be used to light your garden at night, and the one you pulled apart can be used as a solar powered battery charger for AA Ni-CD batteries.