I have the Extra Small Aviator bag. When I saw X3Skier's comment, I thought immediately of the Aviator line. Simple, no structure, but unlike many other unstructured bags, the strength of the bag's fabric gives it some ability to stand up on its own even when empty. I prefer using packing folders and cubes to create my own internal structure, which I can vary depending on the needs of a particular trip.

I've found the XS Aviator, at $30, much more valuable to me than a Tumi bag of similar dimensions that I purchased early last year for over $200.