For people carrying more than the MBA and don't want the bag to look bulging, this small one from Case Logic is just so lightweight and spacious in a small size. I got the 13 inch size for my 11 inch, for reason that I want to yank out the computer and put it back without going through a careful process, to enhance accessibility. In a sense, just enjoying the weight savings without having to telegraph what a small computer is in the bag. After all, I carry the occasional file folder or magazine and don't want them sticking out the top of the bag. This puppy has a front slot zip pocket for an iPhone.
http://www.caselogic.com/14_laptop_...l/index.cfm?modelid=147737&productid=10011382
The one I got from a computer store says on the tag: From 10-14.1 netbooks and laptops / 13.3 inch macbook pro. I didn't see that one on the Case Logic site, but it looks the same as in the image I linked to.