I found this tool to be really useful, had a situation where I had mistakenly deleted an album on my pc, and needed it back off my ipod so I did a google search and came up with this little gem.
I think there are others like it but I used this one and its pretty good, save the interface. Note; this is shareware, it only copies 5 tracks off at a time you have to buy the full version for more usability.