From Research In Motion:
Sync your desktop iTunes music files with your BlackBerry smartphone. BlackBerry Media Sync makes getting more from your music quick and easy!Want a specific playlist for the gym? With just a few simple clicks, you can choose the playlists you want from your collection.
Or, if you just need a mix of tunes to get you through the day, songs can be randomly chosen from your collection. And, to make sure you've always got enough free memory on your BlackBerry smartphone, BlackBerry Media Sync lets you set a limit as to how much--or how little--of your music to sync.