Apple Logic Pro /LogicExpress Discussion

Hi,
I'm looking for a secure backup solution to save my precious data. At 
the moment I backup each day's work on a CD, but can I backup onto 
another hard-drive.
If so, is it best to use an external hard drive, or add another into 
one of the internal slots inside my Mac Pro.
And can someone recommend the best make of hard-drive to buy.
Thanks,
Tristan.