Amazon's Cloud Drive service which costs $20 a year, for 20GB of online storage, now offers unlimited storage for music tracks.  This means you can keep your music in one place, online, and download those tracks whenever you want, to your music player/phone.

They're also offering a free service, which includes 5GB of storage, plus further space for up to 1,000 songs.

For details, on all their plans, look here.