Free song for iPod

Download a program like Limewire or Frostwire that can be used to download music for free, then using that program search for and download whatever music you want. Then open up iTunes and Limewire/Frostwire at the same time and drag-and-drop your songs from your Limewire/Frostwire library to your iTunes library. Then plug in your iPod and sync it.

WARNING: I believe it is illegal in some places, so be careful.

There you go! :D