External USB drives for me. One set of drives is stored in a fire safe at home, one set of drives is stored at the office, and one set is stored at a relative's house in another state. The ones at home get refreshed most often, the ones stored at the office get refreshed about once a quarter, and the one at the relative's house get refreshed during holidays and family get-togethers.

The drives are encrypted (Truecrypt) since they will be outside my physical control. The ones at the office I am prepared to abandon should I get fired/laid-off.