I use the Wenger Synergy laptop backpack (Swiss Army). Bought it for $100 and well worth that price (really well made, protects well and most importantly enough storage room that I have made 2 day trips with it as my only luggage). Now it sells for $50! Gave a couple as xmas gifts so I had the link handy. I looked at a dozen other backpacks and none were superior to the Wenger.
http://www.buy.com/prod/synergy-lapt.../10393071.html