you never said if you're mac or pc. If mac, look at solutions based on rsync. If you're pc, look at robocopy. Both free. They have the ability to copy only files that have been updated and/or only the actual data that's been updated in the files. It speeds up replication drastically.
I've heard good reports on using BackupPC
It uses the rsync protocol for backing up files, and seems to be a bit more newbie friendly than rsync.
Personally, I use rsync, which can be used with Windows as well (via Cygwin). Not recommended for those who are afraid of a command line interface.