attachment for "standard" hair dryers for about $10. I have only tried it a few times, but it seems to work well.
I had to pin the front part a little so it would fit my head better, as it tends to want to cover my face. I think that if I sew in a piece of elastic around the edge, it would fit better and probably dry more efficiently. I really like this attachment, but I wish it was designed a little more efficiently so it would stay on my head a bit better. It works pretty well for drying roller sets (sponge/perm rods that are set wet the night before) that have not finished drying overnight. The end that attaches to a blow dryer fits really well, but can occasionally slip off. It works on my Conair blow dryer, similar to this one:
My hair is VERY damaged but super fine, so it takes about 30 minutes to dry hair that is 75% dry, and about an hour to dry hair that is 50% dry. Just for reference, it takes about 7 (yes, 7!) hours for my hair to air dry. That IS how damaged my hair is! Oh, btw, the picture shown along with the link, is the exact attachment that I bought. Additional attachments and actual bonnet dryers can be found here.
Rating: 7/10 mainly b/c of the design.