Use a CD burner for backups obviously! You can easily get a very good one for under $100 Canadian and blank cd's you can usually get for under $1 each (700MB of storage)
I am buying two identical harddrives, with a "raid" system. Whenever you load or do anything it does automatic mirroring, so one HD is a clone of the other.
The only thing I'm not sure of is if the error occurs during the write process and kills one drive ....does it kill the other...in which case you have a perfect f*ckup...lol