If you are looking for an excellent utility to backup or copy your iPod’s music into your iTunes library, one of the best is Red Chair Software’s CopyGear for Mac.
They come originally from the Windows corner and also offer a tool-set for Windows called Anapod Explorer which includes CopyGear and additional utilities for managing photos on your iPod as well as integrating with Windows Explorer to provide drag-and-drop file management to and from the iPod. Until now I’ve used Senuti to transfer from my iPod, which is donationware. CopyGear is more powerful and well worth the $15 registration fee (you can try it before you buy – by transferring up to 25 tracks before the demo version stops working).
If you want the Mac version, just make sure you don’t do what I did, which was to inadvertently jump to the Windows product page in their store and buy that version before I realised I hadn’t bought the Mac version as intended! You can only get to the Mac store page from the Mac product page.