Tangerine

Tangerine is a new app from Potion Factory that's in beta. It analyzes songs in your iTunes library to determine beats per minute and beat intensity. The idea is that knowing this will help you create better playlists with songs of similar tempo. It analyzed my 5600 songs in a little over an hour and my PowerBook was very usable during that time. It's a pretty app, looking a fair bit like iTunes and you can play songs and create playlists from within the app. It's still in beta and I found a few glitches in the UI and I'm not all that confident about the computed beat values, but if these are corrected, this could be useful.