I bought a very good Ogio Prodigy backpack from ebags.com almost three years ago and have used it extensevely to traverl everywhere. It has provided a superb protection for my TiPowerBook, a Zip drive, an external CD-RW, a Newton Messagepad, cables and allows me also to carry some books and folders.
If you want a little bit more of protection using a laptop backpack, I suggest you to combine it with one of those sleeves that ebags.com also sell. You will end your trip with your laptop as good as new without breaking your bank account