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 our mention from a month ago as the lowest total price we've seen for this model. (It's also $255 under the best price we could find for a used unit in sufficient stock elsewhere.) It features an Intel Core i5-2557M 1.7GHz Sandy Bridge 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 Yosemite).
Note: It features an AppleCare warranty that's valid through December.