Use iPod Classic Without iTunes I use a program called iShuffle with my iPod shuffle. All I do is copy music files in Windows Explorer to the Shuffle's Music folder, then run the little app and it magically works without iTunes.

http://agoraphobeus.free.fr/iShuffle/index.html

Is there an equivalent for the iPod Classic line, and older generations of that line?
You could try using Rockbox, however you might want to check whether or not your iPod is supported. Rockbox is an alternative firmware for your iPod classic that allows you to copy music files just like a normal MP3 player.

http://www.rockbox.org/wiki/IpodFAQ

It even plays Doom!