At Amazon, get a $3 Amazon MP3 Store Credit good toward albums priced at $5.99 or more for free when you link your Facebook account with Amazon's Facebook app. (If you're not already signed in, you'll be prompted to do so; Amazon's app will request permission to post to your timeline.) That's among the best free Amazon MP3 Store credits we've seen. (Though we have seen credits without a minimum price in the past.) Credit expires June 11.