Pandora, Pandora, Pandora. No other service for me worked to reveal new songs and artists I did not know about that nailed my taste. But Pandora relies on manual tagging by music experts. Fantastic, but probably not very scalable.
However, even in the various artist stations, they do play artists "similar to" as well. Which is how I started listening to stuff like Murder By Death, Eilen Jewell, Bakar, Black Pumas, and others.