Groupon offers the refurbished 3-lb. Apple MacBook Air Intel Core i5 1.8GHz 13.3" Laptop, model no. MD231LL/A, for $649.99 with free shipping. That's $350 off list, $111 under our January mention of a refurb (which came with 8GB RAM, rather than 4GB), and the lowest total price we've seen for this laptop. It features an Intel Core i5-3427U 1.8GHz Ivy 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 USB 3.0, and Mac OS X (it's unclear which version).
A 90-day warranty applies, although it's unclear who backs it.