Best Way To Sync A Folder On 2 Drives?

I have an H:/MUSIC on my home computer and I just got a new 1TB external where I'm going to make a MUSIC folder as well, so I can take the drive to work.

Is there a good program where, if I add music at home in my MUSIC folder, or even if I see an error and I clean up an mp3 tag on the external at work, and I take my external home on the weekend, for them to sync the 2 folders up so they're the same? Whether it's a new folder in my home computers MUSIC folder*that needs to go over, or a single*mp3 on the external that needs to be synced to the home computer.

Nice if it's automatic too....plug in external, turn on the switch in the back and it keeps them in sync.