here are some small reviews about ways to listen to music online:
Pandora: Remember when this one came out? It was crazy. I haven't been that into pandora for a few years, and especially now with the ads they put on. The music selection was too repetitious and I often didn't like the things they chose for me to listen to.
lastfm: I don't really get lastfm, except that I know I have an account there and I've listened to stuff. Pretty similar to pandora but I like the selection better. More independent artists, and you can listen to friends' "stations" of stuff they like. You can compile artists you like and they play a selection -- I think. Also, I think there is a way to hook up your itunes to it but I don't know about that.
8tracks: My housemate told me about 8tracks. On this site, you can listen to tons of playlists made by other users. I liked it pretty good for about a day, but then couldn't seem to find any playlists that I found consistently to my liking. There aren't ads, and theoretically this would be a good way to discover new music.
Grooveshark: My other housemate told me about grooveshark, and so far it's my favorite of these sites. You put in an artist or song name, and you can add tracks to your play queue. I don't know how this is legal, but so far I've been able to hear lots of music I've been curious about, but didn't want to purchase. So far I think every artist I've searched has come up in their database. Somehow it searches all music uploads and makes them available. No ads!
NPR Tiny Desk Concert: I love getting these via the "All Songs Considered Podcast." Very famous musicians like Bela Fleck, or lesser known, but talented musicians perform a few songs at the NPR music office. I've liked or really liked everything I've heard here. It has been a good way to discover new music.
Snore and Guzzle Radio Hour: Eclectic hours of music put together by an individual and downloadable to your computer. Thematic descriptions such as: " I’d say this radio hour would be a good soundtrack to accompany the study of the anatomy of flight and bird migration patterns."