MegaMacs offers the refurbished Apple Mac Pro Quad-Core 2.66GHz Xeon Workstation, model no. MB871LL/A, for $559.99 plus $2 for shipping. That's $70 under our October mention (which had a bigger hard drive) and the lowest price we've seen for this refurb model. It features an Intel Xeon W3520 2.66GHz quad-core processor, 6GB RAM, 500GB 7200 rpm hard drive, SuperDrive, NVIDIA GeForce GT 120 512MB graphics, and Gigabit Ethernet.

Note: A 30-day MegaMacs warranty applies. Also, an OS is installed, but it's unclear which version.