By housing two GP (GreenPower) drives, with either 500GB or 1TB each, and using it's built-in simplified software, Western Digital's new MyBook Mirror Edition drives could possibly your "safest" investment ever. You can run with WD's included RAID 1 (mirrored harddrives) or switch it up to RAID 0 (riskier, but increased performance with no data sacrificed) - either way, you'll have an external powerhouse for all of your data needs.
Fans of firewire be weary though, as it only offers a single USB 2.0 jack. The 2TB (or 1TB version of actual usable space) will be going for $550. As for the single 1TB (500MB usable space), it will cost you $290. More information can be found on Western Digital.