Grooveshark is a free music streaming service that gives you the opportunity to upload digital audio files and create great playlists. You can also listen to music uploaded by others.
Grooveshark has streaming features, a search engine and even a recommendation system that helps you to create your own playlist. Over the time the service had lots of problems with copyright law, but the owners won almost every battle.
If you want to listen to free music and upload your own audio files for others, this is the best way to do it, using a simple and efficient way.