I purchased
this one at eBay, which is sized for a Kindle 3 (Keyboard). Mine is black, but I believe there's also one that's clear. The price is $4.95 "or best offer" and it includes a screen protector. The seller accepted my offer of $3.50. As I recall, there are others on eBay that look exactly the same that are priced less (without the screen protector), but I had eBay Bucks about to expire so I went with this one.
It's rather funny because whoever designed this skin must not use a Kindle regularly. If you look at the listing photo, you may notice that the page forward/back button directional arrows are incorrect. That's no biggie, though. It fits like a glove, with cutouts in all the right places for access to the on/off button and ports. There are two cutouts in the back for the speakers.
I have read that some people have a problem with cat hair sticking to the silicone skins. I do have a long-haired cat, and that hasn't been a problem for me at all.
Hah, I did notice the arrows, but I can live with that if it's functional--thanks!