I'm using the neoprene sleeve (8.9" Belkin) I originally bought for my netbook. Kept my Wacom tablet in it after I bought a case that could hold netbook, charger, tablet+pen+cable, etc.
It's not a a snug fit--wasn't a snug fit for the Wacom Bamboo either--but it'll do until I stop being so indecisive about which Kindle case to buy.