You're in look, I just purchased a 13" MacBook, white to be exact and found a few good bags and cases for it.
For a simple slip on case with a small degree of protection from knock and bangs try this...
Very nice find. I wasn't to interested in this game until i saw a few videos and previews on the interwebs and now I can't keep my juicy, juicy eyes of it... this beta will be mine...