Patagonia MLC (Maximum Legal Carry-on) Bag
I travel with this bag and my Timbuk2 messenger bag, and you can carry both on the plane, so you don't have to wait for baggage claim and there's no worry that your bags will get lost. There are great organizer pockets on the outside, where you can easily slip your boarding pass, a book, headphones and ipod, and whatever else you want to get to easily while waiting, boarding, and flying. Plenty of room for a weekend trip. Also, there are hidden shoulder straps so you can wear it on your back if you need to, which I never thought I would until a recent trip to San Francisco had me huffing it quite a few blocks from my hotel to the BART station, and the over the shoulder loop wasn't quite cutting it. So, I decided to try the shoulder straps out and was pleasantly surprised.