One of the coolest little apps that I've seen in a while is Senuti. It's an app for OSX that allows you to transfer files from your iPod to your Mac. Normally, you can either perform a full sync with your iPod or send files, unidirectionally, to the iPod (in "manage my own ipod" mode). But, the feature that is conspicuously missing is the ability to easily move songs from the iPod onto your computer.
Now you can manage your own iPod with Senuti and move files whichever way you see fit.
BTW, I mentioned this in a previous post, but I have been using the Amazon MP3 Downloads service over iTunes lately. It is slightly less convenient because there is no integration with the iTunes player, but the fact that it is DRM-free is well worth the extra clicks to buy from there.