If you're after a thrifty option, this Herschel Backpack will fit the bill. It's a great choice, while not very expensive. Another great option is this SANDQVIST Backpack. It's a product you're bound to love which also doesn't cost a fortune. You may also want to look at this A.P.C. Backpack. This item is not expensive either, but it will make a difference in your wardrobe.
If you want to treat yourself, then you absolutely must check out this Givenchy Backpack. This piece seems costly, but it's worth it. Another product we're drooling over is this Rucksack. It's costly but you get what you pay for. Also consider this Pierre Hardy Rucksack. You won't regret the money spent!