I spent a quite a while searching for the perfect backpack. In high school when I had to carry 50lbs of books around at all times I had an LL Bean indestructible bag, but that didn't work so well when I moved to the big city of Seattle and had to ride metro all the time. I couldn't fit it in my lap and it wasn't water proof. It rains for about 6 months strait in Seattle so a waterproof bag was a must have. I also needed something small and durable that could hold all my art supplies and a laptop. I noticed the Timbuk2 bags on certain design majors and investigated.
Timbuk2 was originally made for bike messengers in San Fransico AND all their bags are waterproof. The price at the time seemed atrocious but as I browsed for bags it seemed that Timbuk2 was the only brand that had everything I needed. I've been happily using my bag for almost a year now and nothing has been better.