Up until recently we used RSync but I found that it wasn't stable enough. We have since moved to RoboCopy (which comes free as part of the Windows Server 2003 Resource Kit Tools) and found this meets our requirements.
It is easy to script via a batch file and can then be run as a scheduled task. We use it to copy data from a remote workers desktop over to his USB drive then over to our server where we back it up, as well as between servers on our LAN.
It will be ideal for your situation.
Take a look at:
http://en.wikipedia.org/wiki/RobocopyHere is an example of one of our scripts:
ROBOCOPY G:\Archive_Drive\ R:\Archive_Drive\ /E /B /PURGE /R:3 /W:3 /NP /TEE