Paribus is a program that links your email account and your Amazon account, and other online stores, and will track price drops and pay you the difference of your original purchase and the price drop!
I bought a Nexus 6 and got back $150 when the price dropped a few days later. No work besides linking the accounts (link the email account where e-receipts are sent, and my Amazon account). When you get an approved price drop rebate, they take a fee of 25% from it.
For Students Click Here – Use your .edu email address and get an extra 5% on your rebates!