As far as quality bags go, Tumi is hard to beat. Yeah they're expensive but I've bought a grand total of 2 laptop bags over the last 10 years, both Tumi's. They've been ridden hard and put away wet, shoved in and out of overhead airplane compartments and kicked and stepped on under airplane seats. I could literally sell them both in mint condition right now, not a scratch or tear on either one of them, even the 10 year old one. So longevity is important to consider when looking at the price tag. Also Tumi's are the best bags I've used for maximizing storage space; they are very well thought out.
Think Tank also makes great bags. The Artificial Intelligence series is a minimalistic laptop bag.