You can transfer songs from your iPod to iTunes library:
First,
*BEFORE you connect the iPod, please go to the iTunes preferences and select "devices", then select "disable automatic syncing for iPhones and iPods"*.
Then, for those songs that you purchased on your iPod:
Transfer purchases from iPod to iTunes.
For all other non purchased content (your own CDs etc), their are ton of third party programs, some is free:
iDump,
Floola. Some is shareware, but they does preserve playlist/ratings/playcounts/artworks etc:
iCopyBot,
CopyTrans