External storage and backup storage is always a complicated issue. I have many external drives from a couple of USB keys up to a full Ethernet connected external 500GB drive. Brando appear to have what would be a perfect solution for me.
If you go to their website you will see they have docking boxes that allow you to plug 2 SATA hard drives in and then connect them to your computer using either eSata or USB. They come in a variety of flavours including some with a plethora of card slots and video outputs. However this one I have linked to support 2 drives via the eSata interface and costs $63. I can then buy bare hard drives and swap them as needed. I will be ordering one of these in the near future and will provide a full review of it here.