This free plugin (Mac only) allows you to plug in your iPod and copy all the music of it to your library, which Apple specifically forbids. Because it would enable pirates, and you know, be useful from time to time if you use multiple Macs but don't keep the library the same on each one. Maybe it's just us, but we've got this weird feeling that the plugin won't be around for too long.
Update: We called it, Apple had the developer's ISP remove the file. Too bad it's already on another site here.