I cannot sing the praises of Tom Bihn enough.
www.tombihn.com.
Fabulous bags, so very very well thought out. I have the brain bag and it holds my Macbook Pro, my QE2s, big bag of cables and flash drives and power supplies, my pashima, a book, DVD case, a pack of clothes incase regular luggage fails to make it, my medicines, etc. It's completely wonderful top to bottom.
^ ^ ^
Agree completely about Tom Bihn bags. Mine is not a backpack, I have the Empire Builder shoulder bag--but it is equally well-thought-out and all but indestructible. The waterproof zippers alone (Tom Bihn is based in Seattle, so waterproofing is a priority) are worth the price. Everything I need to carry for work fits in a logical place, and I can get to almost everything in the bag with one hand, without having to take it off my shoulder. I only wish they made a rolling briefcase, for those weeks when I have to carry
two laptops.