MP3Tunes is a great service. It allows you to upload all of your music to the cloud, and then you can play it on any internet connected device. Previously, you had to do all that uploading from your computer, and you would be able to play it on your Android. On Monday, MP3Tunes just updated their app so that now you can upload from your Android to the cloud and play it on your computer. This is great for people who have purchased songs on their phones such as with the Amazon MP3 service.
They posted a video of this in action, where a song was uploaded on an Android phone and played with an iPod Touch. It is embedded below.
MP3Tunes will give you 2GB of cloud storage (your "locker) free. Beyond that, it is a tiered system that you can understand from this fancy chart, courtesy of MP3Tunes: