iShoppingdeals - Black Soft Silicone Skin Cover Case + Screen Protector Film + Smart Headphone Wrap for Sony Reader Pocket Edition PRS-350
This is exactly the sort of grippy, protective skin I was looking for for my PRS-350, and as far as I know, or certainly at the time, the ONLY one of its kind, and you certainly can't argue the price.  The bonus screen protector was nice too (although it causes glare, I'm using it for the moment).    It is on the soft rubbery-side, but it's a perfect fit.  I'm happy with it.