Customers often ask for recommended software to perform backups. We do not have any commercial ties to the following solutions, but based on their established reputations they are worth considering for use with either with an external disk or a network file server.
A fully featured, but free, solution is Ace Backup:
A simple "sync" application is available from microsoft, called Synctoy. It is simple to use to set up a "folder pair" that is kept in sync between your desktop and remote folder.
If you want a proper enterprise solution, then leading commercial solutions are: