you could try a search
this is a pretty well covered topic
like in this thread
that said.. most people here seem to like Super Duper
I've used SynchroniseX and it works well for me (but it's not free).
there also used to be a freeware app that came with Lacie drives, but it seemed a bit clunky last time i looked at it - SilverKeeper - they have 1-click too. Likewise PsynchX and iBackup, but it depends a bit on how you want to do backups and what level of convenience you're willing to pay for. Download and trial is probably your best bet.