Radio, motion pictures, television, or other forms of mass media
Commercial Streaming Services (Spotify, Pandora, etc)
Vinyl Community Social Networks
Torrent search aggregators/featured private torrents/manual searches
Music literature and/or periodicals (online or in print)
Friends (the real social network)
Attending local performances / music events
Subreddits like r/listentothis
Crate digging for intriguing mystery albums
Recommendations from your local indie record store gurus
Following independent music blogs or sites like Hypemachine and Pitchfork
Recommendation engines like Gnoosic, Allmusic, etc.