Maybe someone, somewhere doesn't yet know of this great site. Pick an artist or song, and Pandora uses its Music Genome Project roots to pick other songs you'll like. Save as many stations as you like, so that when you're feeling moody, you can pick the station to lift you, or deepen that mood.
There are also hacks that let you save Pandora's tunes as MP3s on your computer. There's one described here.
