I had a need to update my movie and songs list today and was looking for a tool that would ensure the song lists updated in my external drive and my laptop hard disk. Found this simple Microsoft tool SyncToy. You can choose two independent folders ( left and right folder ) to keep your data in sync between folders.The best options that comes with this tool

1. Two way syncing also Echoing a particular folder / Subfolder.
2. Very simple and intuitive UI.
3. Also you can create many pairs of folders and you can run the pairs whenever you need to / schedule the synch.