Jandd and Ortleib also make messenger bags. I use a Timbuk2, and I like it fine. I don't like to load up too much w/ books and other heavy crap, though. Shoulder bags just don't have the balance and support for that, so I usually carry my lunch, rain and emergency bike gear, and maybe some paperwork, plus misc stuff like phone, sunscreen, etc. and it's plenty heavy...but it's sweaty on your back in hot or humid weather, and a cross-strap of some type is essential to keep the bag from shifting...I'd either go with a backpack or panniers for heavier loads like lots of books...