SoundCloud is a free social web app for sharing your musical creations with the world. Upload your tracks and mixes, and they will be playable from browsers.
There are lots of filesharing services, but SoundCloud is dedicated to music and this specialization makes it much more convenient. Once registered, you can upload up to two hours of music in AIFF, WAVE, FLAC, OGG, MP3 or AAC formats. You can share your music publicly or privately, and even make your track downloadable.
The social part of SoundCloud is similar to Twitter - you follow members and others follow you. There are also groups, so you can find people with similar tastes to you. Soundcloud looks cool, is easy to use and has great tutorials to get you started. Sharing your music in Facebook will actually let your friends listen from Facebook itself, with a little widget. It's a fantastically simple way to share music.
With great sharing options and excellent design, SoundCloud is one of the best web apps for anyone who wants to show of their tracks and DJ mixes.