Backpacks

My backpack has finally started wearing through on the bottom. I thought a simple Wal-Mart run would yield a similar backpack, as that's where I picked up my current one and the nearly identical one before that, but the ones they had were all too damn small. Most of them were, at best, 75% the same capacity as my current backpack.

Is it really that unusual to want a backpack capable of holding a laptop, 3 ring binder, several textbooks, headphones (real headphones, dammit, not shitty earbuds), various cables, and several smaller misc. items as well as doubling as a decent piece of luggage for weekend trips? Does anyone have any recommendations for large, reasonably priced backpacks? I've been toying with the idea of a messenger bag, but I've yet to see any with a similar carrying capacity to my backpack.