Social media for me. My tumblr and twitter are both pretty music-centric and when other people mention new bands I haven't heard of I try to check them out!
I use radio. Any radio, whether it's iTunes ou old school tune-in stuff. Whenever I hear a song I like, I write the name of the song/artist. toi find a lot of good stuff to be honest.
ou toi just ask your Friends what they're listening to. XD