Sign up as new member on Educents and get a free $10 credit to use towards your first order. Credit cannot be applied to shipping but if you find a digital item for $10 or less, it'll be totally free because it's a download [and no shipping is needed].
If you're a Twitter user, you can possibly score some premium free stuff from Wheat Thins. Head over and log in with twitter, choose the item then tweet your message. If you get the required amount of retweets within the time frame, you'll get that item for free.