Other World Computing offers the used 3-lb. Apple MacBook Air Intel Core i5 1.7GHz 13.3" LED-Backlit Notebook, model no. MC965LL/A, for $649 with free shipping. That's tied with last week's mention of a used unit as the lowest total price we've seen for this model. (It's also $167 under the best price we could find for a refurb.) It features an Intel Sandy Bridge Core i5-2557M 1.7GHz dual-core processor, 13.3" 1440x900 LED-backlit LCD, 4GB RAM, 128GB SSD, AirPort Extreme (802.11n wireless), Bluetooth 4.0, Facetime camera, Thunderbolt, and Mac OS X 10.7 Lion (eligible for free upgrade to Mavericks).
Note: It features an AppleCare warranty that's valid through December.