I just bought a case for mine that was designed for netbooks. (I'm a knitter so I carry my knitting around, rather than my book, but I like to have it if I'm going to be away from home overnight.)
My local Target store had them on clearance for $5 (vs $20). It's a little bigger than what I need, but I figure if it was intended to protect a netbook with a big expensive screen, then it will work for my reader too, right? I have the light wedge cover and it all fit easily.
It's a girly design
but as long as netbooks continue to become popular, cheap padded carrying bags should become more widespread.