If you want to create a playlist that songs which match each other, you could do it the slow way, which is to go through your entire song library in iTunes and manually add them, or you could use this cool thingy from Potion Factory.
These guys are behind Podcast Maker(drag and drop to create podcasts in a cool snazzy interface) and Voice Candy(alter your voice with funny effects).
Now they’ve made this thing called Tangerine, which analyses your song files to determine their beat and beat intensity. Then, Tangerine can create playlists based on what kind of playlist you want to have: upbeat or relaxing.
Its currently in free beta right now, so give it a try!

2 Comments
Oooh, very promising. Eventually one of the things I hope to resolve is - the ability to search by tune - one forgot the title but remembers the key melody (probably online, not for a hard disk.)
Hi,
Thank you for blogging about Tangerine. We want to send you a license as a token of gratitude, but we can’t find your email address.
Please contact us. Thanks!
- Andy