I'll bet you already have it.
standard unix util.
However, beware old style files with resource forks - rsync doesn't understand resource forks.
That said, I use it (along with cron) for a poor man's backup tool to sync a mirror of my cvs repository to an external drive.
"Whenever you find you are on the side of the majority, it is time to pause and reflect" --Mark Twain
"The significant problems we face cannot be solved at the same level of thinking we were at when we created them." --Albert Einstein
"This is still a dangerous world. It's a world of madmen and uncertainty and potential mental losses." --George W. Bush