All of our files are stored on a central file server and shared to each person from there. We use a simple program called Backup Magic to copy the entire data drives of the server to two external hard drives. The first external drive is backed up daily automatically and remains on site, and the second drive is backed up every two to three days and taken off site.
Backup Magic is very easy to set up and use. It basically sets up a script to copy everything from one place to another, and you can set the backup type such as mirroring, which will move over any new or changed files, and also delete from the backup files that you have deleted in the main data folder making an exact duplicate of the source location.