A plastic DVD case is the perfect size. I cut out the thin plastic walls for holding the DVD in and taped some fabric on the inside. Perfect size, protects the KOBO inside the stuff, light plastic. Even fits in the pockets of my jackets.
I also saw a little Outdoor Research bag that was snug but did fit. They have a couple sizes. It's lightweight and would need something to protect the screen like a piece of cardboard or something.
http://www.outdoorresearch.com/site/...rganizers.html