Tilly's
Hot Topic
Sport's Authority
Target
Aeropostale
Roxy
Volcom
Hollister
Abercrombie
PacSun
I really like Roxy's backbacks. I got a Roxy backpack at their store, but they have them also at Tilly's. Tilly's is absolutley the best place to buy backpacks because they have messenger bags, totes, and plain backbacks. They have girly girl stuff as well as tomboyish stuff and its like $20-$30. They also have lots of good brands like quiksilver, roxy, volcom, hurley, and jansport for backpacks, and good designs. Hollister and Abercrombie have big totes that are sturdy, cute, and you can fit a lot of stuff in them too.
Hope this helps!