1. Google Play
Google Play gives listeners the chance to upload and store thousands of songs from their own collections for free, create playlists, and listen to hundreds of thousands of songs in a huge variety of genres. You can listen for free to the Google Play radio offerings; users have the ability to subscribe which makes the experience ad-free. More »2. Hype Machine
If you're looking for something to expand your musical tastes, Hype Machine is a great choice. This innovative site gives listeners the ability to find new music via people who are writing about the music that they love - all in one place, rather than skipping from site to site. More »3. Shoutcast
Shoutcast gives listeners the ability to listen to over 70,000 stations in a huge variety of genres, from Alternative to Talk to Holiday. However, that's not the only thing you can do with Shoutcast - if you want to start your own radio station here, you can, with free broadcasting tools made available by the Shoutcast service. More »4. Accuradio
Accuradio makes listening to music online simply fun. They offer the standard genres of music, but they also offer enjoyable "channels" that change every so often and are a great way to discover new music. More »5. Slacker Radio
Slacker Radio gives users the ability to search by artist or song and stations will be suggested, with the ability to craft that station into exactly how you'd like it to be. There are different payment levels available here, but most of the features are absolutely free and listeners can take advantage of hundreds of stations. More »6. iHeart Radio
Think of the sort of music you like, and iHeart Radio will suggest stations for you based on your preferences. You can also use iHeart Radio to listen to local stations all over the United States and Mexico, create stations based on popular artists, or discover top podcasts on a wide variety of subjects. More »8. 977Music
977music.com is 100% free for listeners, and you can listen to as much music for as long as you would like. There are hundreds of channels here programmed by listeners, and they are available wherever you might have Internet access - both home and work. More »9. RadioTunes
RadioTunes is one of the most popular streaming music sites on the Web. You can filter your musical tastes by Style (Smooth Jazz, Easy Listening, Top Hits, etc.), and Channels (80's, Mostly Classical, Oldies, etc). There are seemingly unlimited stations to listen to here, and listening is free (must sign up for a free account). More »10. Radio.net
Radio.net is a great service; you can access all sorts of global broadcasts here, from the BBC World Service to Radio Swiss Classic to CBS Dallas. More than 30,000 radio stations, online radios and podcasts are available here to listen to within the USA, Canada, Europe, Australia, and more. More »11. Last.fm
Last.fm offers listeners the ability to not only listen to and discover music, but also visualize the listening habits and musical trends that the Last.FM musical community is listening to. It's an interesting way to see what other people are listening to. More »12. Soma.fm
You can listen to Soma.fm's stations right within your Web browser, just like all the other streaming music websites on this list. There are only a limited amount of stations here, within highly specialized genres - jazz, chill, indie folks, etc - all featuring a very California-like vibe. Soma is especially popular with people looking for background music for tasks that require concentration. More »13. PublicRadioFan.com
PublicRadioFan is a massive collection of stations around the globe. You can search by schedules, time zones, station call letters, and more. More »14. Pandora
Pandora lets you create your own radio station, from music that you choose, and then you can continue to improve upon the service's selections as it plays for you. Thumbs up for something you like, thumbs down for something you don't. More »15. Spotify
Spotify is somewhat similar to Pandora, at least in concept. Spotify functions more of a platform on which you can install and use different musical applications, such as Billboard's Top Picks, Rolling Stone Music, Share My Playlists, and Digster. You can listen to entire albums without paying for them (with only limited commercial interruption), create playlists, share your favorites with others, and more. Radio stations are also available on Spotify, but you create them yourself from songs you already like. More »Source: http://websearch.about.com/od/musicsearc1/tp/Free-Streaming-Music-Online-The-Top-15-Websites.htm
Honorable Mention:
Internet-Radio.com
With thousands of radio stations around the world, there is something here for everyone.