Replying to Ipod transfer programs?

what's the cheapest, best program for transferring music between an ipod and a computer without losing all the music on one of them? are there any free ones? i've tried a few with free trials but that ends up shitty. recommendations? i don't mind if i have to illegally download something, i've been mad desperate to get this plus i just lost an ipod video that i had for 3 years. btw i searchbarred for this but didn't find what i wanted. thanks