Libra is a very simple application that allows you to create, use and manage multiple iTunes music libraries. Normally, iTunes has only one library, and you can create playlists and groups within this unique library. However, some users have reported that iTunes slows down noticeably when the library becomes large, and other users would like to simply categorize their music in separate sets. This is what Libra allows you to do safely. (Mac & Win)

even more yeah:

IdleTunes is a fantastic new piece of software for Windows which fills in the iTunes feature gap and makes managing your music even easier. (...) ability to add iTunes playlists into any MP3 player, better playlist creation and control, (...) automatic removal of dead or missing tracks (Win only)

via TipMonkies, schicke Site, BTW.