When you want to listen to music, but you don't know which music, where do you go?
Last.fm takes the things you've listened to recently and recommends a range of similar music, based on what other people have been listening to. You can see the recommendations on the web, through the API, or in the Spotify app.
This Is My Jam
Alternatively, find people with good music taste and see what they recommend. Follow people on This Is My Jam and get a feed of their chosen tracks, either on the web or in the Spotify app.
Add Spotify users to your "People" list, and it shows what they've been listening to - click on any of the tracks they've played to start listening.
Not just listening to live radio, or listening-again to recorded radio, but generating playlists from the latest broadcasts. Subscribe to playlists of your favourite shows in Tomahawk or in Spotify via Britify and have the latest tracks available at all times. Alternatively, subscribe to a radio station and use their playlist as a seed for new exploration.
Find some broadcasters that you like on Mixcloud (e.g. The Quietus, or many of the Resonance FM shows are archived here), and follow them to get their latest mixes. Each mix has an accompanying tracklist, and it's fairly easy to link each artist to Spotify/Tomahawk for further exploration.
There are Spotify apps for The Guardian, Pitchfork and the NME - among others - which list the albums that they've reviewed. Even better, set your own filtering criteria in Spotimy or Biblify for albums reviewed by a whole range of sources.
Location and Venues
Songkick maintains lists of all the concerts in a particular area. If there are some venues that you know usually book good musicians, you can listen to tracks by everyone who's going to be playing at those venues, either in the Spotify app or on the web.
More Like These
These Spotify apps let you create playlists of whichever view they're currently showing - other people's recommendations, reviews, tracks you've liked previously, etc - but there's one more killer feature:
Essentially, this takes the current playlist and performs a "More Like These" query (via The Echo Nest), generating a new playlist of similar tracks.
Thus, music discovery goes from an initial seed source (people, robots, or a playlist in a certain style), narrows down for more detail (selecting a specific artist or album to hear more of), or widens out (related artists, playlist radio) for exploration. Sooner or later you'll hear something that sounds just right, and you can feed it back for other people to enjoy.