Dick's Sporting Goods offers the Under Armour Hustle 3.0 Backpack in several colors (Black/Steel pictured) for $39.98 with free shipping. (Zappos offers it for the same price.) That's the lowest price we could find by $15. It's water repellent and features a laptop sleeve, side pockets, and a shoe pocket.

Update: Shipping is now $5.99; however, Zappos still offers it for the same price with free shipping.