MegaMacs offers the refurbished Apple MacBook Intel Core 2 Duo 2.4GHz 13.3" Laptop, model no. MC516LL/A, for $549.99 plus around $20 for shipping. That's $249 under our December mention of a used model and the lowest total price we've seen. It features an Intel Core 2 Duo 2.4GHz dual-core processor, 1280x800 LED-backlit LCD, 2GB RAM, 250GB hard drive, SuperDrive, AirPort Extreme (802.11n), Bluetooth, and webcam. Deal ends March 19.
A 30-day MegaMacs warranty applies. Note that it's not clear which Mac OS is installed.