I looked around quite a bit but all the ones in the big retail stores (Best Buy, Target, Meijer) are cheap or ugly or both.
One suggestion (seriously) is the Apple Store. The Macbook Air has an 11.6" screen and is about the same thickness as the SP3 (w typecover) So sleaves and cases made for it should fit pretty well.
Another suggestion is if you have a college campus nearby, look for the local Student Book Store.