Dont Want to look like a nerd?
Ok so all the book bags that others have posted look like the worlds biggest nerds, sorry I dont want a square box on my back.
Check out The North Face bag Borealis , this works great for my powerbook. It is offered in 8 colors
http://www.thenorthface.com/media/gear/catalog/AMC4/AMC4-417_mag.jpg
http://www.northwestoutlet.com/images/AMC4.jpg
Front bungee system with reflective hits
Utility pocket fits a laptop and hydration system
Laminated backpanel with breathable mesh
Hydration sleeve and hose port
Tuck-away hipbelt
Small stash pocket with water-resistant zipper on front, (store an iPod)
Front pocket with organizer
Dual mesh side water bottle pockets
#10 YKK® zipper
Safe-T whistle on sternum strap
My girlfriend uses this one
http://www.thenorthface.com/media/gear/catalog/AMC2/AMC2-417_mag.jpg
Large front mesh pocket
Padded laptop sleeve
Laminated backpanel with breathable mesh
BackSaver angled front panel
Tuck-away hipbelt
Small stash pocket with water-resistant zipper on front
Front compartment with organizer
Dual mesh side water bottle pockets with reinforcement
YKK® zipper on main zipper
Reflective hits
Safe-T whistle
These paks are like the best b/c you can use them for multiple things and can carry anything that can fit inside and still be comfortable on the back.
Also get a sleeve like others are saying, sometimes you may not want a book bag on your back. Also check out
http://www.booqbags.com/Detail.bok?no=1409 for GREAT sleves.
http://www.booqbags.com/stores/booqbags/images/BillingSet/VXM-BLK-XXX_0003.jpg