Speck Hard Cover for MacBook
http://www.speckproducts.com/13mac-seethru.html
I've read a few comments regarding the extra plastic from the cover preventing the display of the MacBook from opening as far as it normally would without the cover. I just haven't seen any comments regarding how much of a difference it makes.
PROBLEM-FREE BlackBook - Black 4GB Nano - Black 8GB Gen 2 Nano, Mac OS X (10.4.8)