I am in the process of reviewing a bunch of solutions.
Easiest? Get a SATA RAID controller with two eSATA ports. Create a RAID 1 across them. That way you won't depend on any particular enclosure. You may want to RAID 1 your internal drives as well, since you'll have unused internal channels. I would recommend staying away from proprietary dual-drive units. Specifically, do not even consider Western Digital MyBook and Maxtor Onetouch III Turbo. If opening the unit to replace a drive voids its warranty, you don't want it.
If you need yet more space, as digital media workflow tends to produce, a larger array may be appropriate. You can use inexpensive SATA drives in them. Inexpensive RAID controllers are easiest obtained as part of a Dell server that's a few years old... They also make for excellent NAS boxes.

Another option is an enclosure with a SATA port multiplier and a RAID controller that supports them. Then again you can go with a network box, which is basically a dedicated computer, usually powered by Linux, with a hot swap cage.
I am writing a book on this subject (multi-tier backups for home users).

Be careful, dual-drive units tend to be setup for RAID 0, which you do not want.
Data recovery companies always have a confidentiality clause in the agreement for any work done.