Mom's by Heart has posted a great list of Back Pack Deals! You should go and check out the HUGE list!
I really like buying a really good quality back pack for your kids that will last a few years instead of buying a cheaper pack every year or even twice a year! You can add sew on patches, zipper pulls and pins for the extra cool character that your kids crave. But take the back pack (even if you order it online) and pull at the seams where your child will put the most wear on it. Like the handles or the bottom of the bag. If you can pull apart the seams and see the thread give the back pack won't last. Don't purchase those or send them bag in the mail for an online purchase. It is not worth it.