I have a 320gb external WD drive and i am looking for suggestions on which is the best free backup software to use.

They are many free back up software: one is already built in the Mac OS such as Time Machine.

It is pretty simple to use and quite good. WD Smartware is also good and simple to use. Its put file to each category like Documents, Picture, Music, Movies, Mail and other file type for you.

However, as a user you still need to learn to get familiar with the features on each software.

Copy and paste is still the best way, as long as you know how organize them.