Drag and drop is what I use. But the Motorola Media Link is a great syncing solution if that's your fancy. The Media Link application will also give you the option to automatically transfer new pictures, videos, and music to your PC as well.
I have had no luck with doubleTwist as it does not appear to support sync'ing media stored on a mapped drive (I keep all my media on a NAS and mount accordingly). Any suggestions that doesn't include direct copying? Ideally a solution needs to include photos, music, video, etc...