I have a completely NEW case for a 13" MacBook Air. I have the black color (see link).

It is a very nice design, it still protects your laptop while letting it remain slim, as the MacBook Air was meant to be. Ended up not using it because I got a backpack with a built-in laptop compartment, so selling it off cheap.

Original price: $30
Selling for: $20

Pictures in link below:
http://www.incipio.com/MacBook-Air-13in-Cases-Accessories/Incipio-MacBook-Air-13in-Slim-Sleeve-Case.asp