Parts list:
1 plastic mixing/serving bowl, approximately 12" diameter - $1.50
Velcro (I purchased a 6 foot length because I knew I would be needing more later) - $6.25
Tape - Had laying around, been a while since I bought any so don't know prices, lol
Aluminum foil - You will need about 2-3 sq foot total, especially if you are as prone to screw ups as I am - About $.25 worth out of a roll
Scrap cotton: Either an old white t-shirt, rag, etc, as long as it is thin and white - free
Sorry I got too involved to do pics as I went, but the process is fairly simple.
First, trace the outline of your flash on the base of the bowl, as centered as possible.
Then, using a utility knife, cut out the rectangular hole (the plastic will most likely chip and crack, I used large portions of duct tape to reinforce once I was thru with the hole :D )
Third, place your flash in the hole and use your velcro to secure it to the bowl (I had to wrap the edges of the hole in duct tape a few times to get a snug fit for the flash head)
Fourth, line the inside of your bowl with aluminum foil, tape it in place.
Finally, stretch your cotton over the outer edges of the bowl, securing with tape as you go.
Here are a couple of example pics:
Yeah, I need to get some windex on that mirror ASAP, lol, it's the guest bathroom so I been neglecting it

By
davidmsager at 2011-06-28
Looks to be getting pretty good diffusion, time for a test shot, held at arms length, firing the flash manually with a 1 second exposure since my radio triggers have not yet arrived:

By
davidmsager at 2011-06-28
It ain't pretty, but it works:

By
davidmsager at 2011-06-28
I am going to come up with a way to pretty it up a little bit shortly. I also have a quick cardboard snoot setup I made, but that is pretty self explanatory. My total investment for flash, radio triggers, beauty dish and snoot = $50-55