US: 25 holiday songs, one released each day until the 25th (For people with US billing addresses only)
UK: 3 pounds-worth of mp3s (your choice!) on December 25th and 26th only. Use the code "FREEMP3S" at checkout. Can also be used as three pounds off downloading mp3s worth more than that. (For UK customers only.)
Amazon's mp3 download service has finally gotten me to readily consider buying mp3s as an alternative to buying CDs. iTunes didn't do it since DRM-free files cost extra (although I still download their single-of-the-week). My fuzzy awareness of other DRM-free music download sites was that they required subscriptions, with which I couldn't be bothered. Amazon's a company I know, so much as they're already getting too much of my spending on other purchases, it was very natural to extend that customer relationship to music once the downloads became available.