I am ready to give you some advice. It's not cheap, but definitely mature solution. First of all - all solutions based on HDDs are not dedicated for backup and archiving, but for on-line storing.
There are 2 options for archiving: tapes and magneto-optics. Tapes usually using in huge enterprise-class solutions, not for us.
But magneto-optics is dead, you can say... Good news from me - it's not.
By Fall 2012, Sony will be releasing new stand-alone drive unit equipped with a USB 3.0 interface and storage capacities between 300GB-1.5TB.
It's not very cheap, but it's convenient, reliable and OK for long-term storing. I plan to buy this device and use it to archive all my audio and video media.