Moodagent has only been out about three weeks and already has over 200,000 downloads and is currently averaging 25,000 downloads a day. Pretty impressive. It's a freebie that lets you move sliders to indicate the type of music you want to hear, and in seconds it generates playlists. It uses the song's actual content to make recommendations based on digital analysis of the music. This is in contrast to Apple's Genius, which makes recommendations based on purchase history. Plus, even if the metadata about a song is missing in your library, Moodagent can still find it, because it's based on the sounds themselves rather than song info.