If you are on a tight budget, your best bet is this Bric's Backpack. It's a wonderful item, while not very expensive. Another wonderful option is this Herschel Rucksack. While the price is not too high, be sure that this item will become an excellent addition to your wardrobe. Or you can choose this Kenzo Backpack - be sure you'll be making a stylish addition to your wardrobe.
If you want to splurge, then what you're looking for is this Burberry Backpack. It's more expensive but worth your money. While you're at it, also have a look at this Valextra Backpack. Yes, this item is expensive, but it does not mean it's not worth it. It is also worth checking out this M2Malletier Backpack. You won't regret the money spent!