If you're not planning on spending much, you'll appreciate this adidas by Stella McCartney Rucksack. It's a fail-safe choice and a great investment. You might also want to check out this Backpack. It's an item you'll fall in love with which also doesn't cost the earth. You might also want to consider this Kenzo Rucksack. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.
If you're not a thrifty type, then what you're looking for is this Burberry Backpack. It's more expensive but worth your money. Another product we're drooling over is this The Row Backpack. It's costly but you get what you pay for. And one more item you might be interested in is this Chloé Rucksack. 'Cause you deserve nothing but all the finer things!