If you are a fan of music, especially discovering new music, you might want to check out 8tracks. While I am linking to their site, I have never actually used the site itself, as it is one of many sites blocked where I work. Thus, I have been using the app on my Android phone (there is an iOS version as well). The idea behind 8tracks is that real people are better than computers at creating music playlists, so the site is a big collection of user created playlists. It is not a place to go to if you want to browse for new albums, listen to an entire album, etc. While I listen to more albums than playlists, I find I am using the 8tracks app on my phone more and more. I would compare 8tracks a little more to something like Pandora or Slacker (than say Rdio, MOG, etc). There is also a nice social media kinda thing built in. If you come across a playlist you really like, you can "follow" the person that created it, so that all of his/her playlists show up in your "mix feed" (which also is a good way to notice when that user has added a new playlist). To enable discovery of similar playlists, you can browse tags (like the tag cloud on my blog) to find other playlists that are similar to the one you are listening to. The search options are one of the strong points..below is a list of some of the search/browsing options within the Android app:
-Mix Feed: all playlists by the users you follow
-Liked Mixes: playlists you have "liked"
-browse by tag
-Hot: these are playlists getting a lot or recent play/likes
-Popular: playlists with lots of likes/plays
-You can combine some of the above, too. So for example, you can select "hot", then filter to display a certain tag like "indie"
There is a pretty diverse selection of playlists, as some of the most popular tags are sleep, study, indie, workout, driving, summer, etc. As you can see, the tags are not just used to describe genres of music. They are used to describe a mood or activity that fits the playlist, too.
I have found it to be a great app for finding good music, as there are lots of fantastic playlists. And I agree with their premise that real people create better playlists than a machine. The app is free, though I believe they offer a subscription. I just use the free service, which does have ads within the app, but not in the audio (so no audio commercials between songs..not that I have heard anyway).