Most dependable cheap(?) backup system

Many of my clients want a backup for thier systems. Most backup systems are over 650mb and we are talking about computer iliterate people so I dont think a CD-RW setup would be good for them. The only two other options I see are a second drive or tape backup system.

I do not know what in the mainstream is dying out, if anything, and I would like to know what the standard dependable unit is/would be. Also, I dont think software like Veritas is in the budget as most of my clients are home owners (one of the key words here).

Can you all give me some opinions and ideas? Thanks.