UniDays offer a boatload of student-exclusive offers and discounts in hundreds of stores, either on the high-street or online. It's a completely free service, you just verify that you're a student using your university email address or college email address and then login.
Offers regularly include 20% off Topman/Topshop, 20% off River Island, 15% off Apple, 30-50% off Boohoo, 20% off New Look, half-price Spotify, and freebies sent to your emails!
They have a great app too that can be used anywhere.
*Get bonuses when you register!*