There are several ways out there. Here I'd like to share some that I've tried and found convenient.
1) use your iPod to help you transfer.
If your songs were purchased from iTunes store, simply "Transfer Purchases". If your songs were from other source, use this iPod to iTunes transfer program to help you http://ipod-tool.com/ipod-software/ipod-itouch-iph...
2) use iTunes to iTunes transfer software to help you transfer.
It is an easy to use iTunes utility designed to help you backup/recover/transfer your whole iTunes library and media files. It offers a simple way to keep your iTunes in sync everywhere. You can use it to backup your own iTunes library or synchronize multiple iTunes on different computers. The backed up library file is pretty easy to transfer to other iTunes, and it's easy to manage.
Hope these can be helpful to you.