Looking for somewhere to upload your music and get it heard by people? I've put together this list of places where you can upload your music today. All of them are free or have free versions of accounts. I have sorted them by how popular each site is, so expect more listeners at the sites which are listed higher up in the list.

MySpace - We all know this one, still very much alive and almost essential for musicians to have a profile here.
IMEEM - Change a standard account into a musicians account and you can start creating your artist profile.
Last.fm - Allows you to see how many people are playing your tracks, you can also upload full tracks or clips.
The Internet Archive - Not just music, but you can easily store your own music tracks on here for people to download.
SoundClick - Upload your music, widgets for your music and genre separated charts based on plays.
MP3.com - Upload your music for listening via streaming or download.
Jamendo - Upload your music and release it under a Creative Commons license.
OurStage - A site which puts your song into genre specific contests and allows listeners to vote for your tracks against other tracks.
ReverbNation - Create your artist profiles and site includes loads of widgets giving you the ability to integrate your ReverbNation into Facebook, Bebo and more.
PureVolume - Signup to create your artist profile and upload your tracks.
SoundCloud - Allows you to upload, share and also receive tracks. Free users can upload 10 tracks for listeners.
MusicForte - Caters to independent musicians and allows them to sell their music online inlcuding sheet music.
Virb - This one is not just for music but there is a lot of people who do use it specifically for music.
Amie Street - An interesting site where your music starts out being free and as it gets more popular it increases in price.
TheSixtyOne - A site where listeners are playing a game for points and voting for your tracks if they like them.
BroadJam - A social network where you can win prizes and explore licensing opportunities in TV and film.
GarageBand.com - More of a review system, but your music will still get listens and therefore exposure.
Fairtilizer - Upload your music and gives you a single player for all your sites and has charts based on plays.
iSound - Upload your music, videos and photos and create an online profile.
CCMixter - Upload your music if it is licensed under Creative Commons for others to download and remix.
mTraks - Music community for independent artists to promote their traks.
Humble Voice - Another place to upload your artistic creations, not just for music though.
Jukebox Alive - Another place to upload your music to, list your gigs and publish your music bio.
ArtistServer.com - Another place to upload your music and create an online presence.
Unsigned.com - Create your online profile and from the name I presume it is best to be unsigned .
Muzic - Upload your music and it could become the free and legal mp3 of the day in the mp3 jackpot.
WorldSings - Upload your songs and the best 20 throught the year will get to compete in a song contest.
Tribe of Noise - Get exposure for your music and get listened to by the industry.
World's Best Producer - Battle to become the worlds best producer for each month throughout the year - mostly HipHop based.

If there is any notable sites that I have missed and I'm sure there are, please add them to the comments and if I think they are worth listing I will add them to this list.