Normally music review websites. If something gets a good grade, and I'm in the mood for discovering new music, then I'll often have a gander on over to Spotify or YouTube and have a quick sample. If I like what I hear, I'll listen to the full album in question; if I don't, I'll normally stop there and not think about that artist/band again. If I like the band/artist and discover that they have an extensive back catalogue, I'll also try to listen to as much of it as possible, as I tend to binge on new music when I can.
For me, the best things are year-end best lists. Things like Pazz & Jop, or lists from Pitchfork/Drowned in Sound/The AV Club are a really great place to start. I certainly won't agree with all of them (last year I sampled 10 new records based on their positions in year-end best-of lists: loved 2 of them, liked about 4, and disliked the other 4). It's because of this that most of my new music discoveries normally happen months after the records have been released; I just won't know about them until the end of the year!