Apple Mac Pro, A1186. The fastest of the initial debut, this 2006 Mac Pro Quad Core 3.0 features two 3.0 GHz dual core Intel Xeon 5160 processors with 4 MB of shared level 2 cache per processor, a 128-bit SSE3 vector engine, and 1.33 GHz "64-bit dual independent frontside buses."
Goodies include a 500MB hard drive, 4 GB RAM, SuperDrive, ATI Radeon HD5770 1024MB video card with a dual link DVI port and two Mini DisplayPorts.
Ports include dual Gigabit Ethernet, five USB 2.0 ports, two Firewire 400 ports, two Firewire 800 ports, and optical digital audio in/out.
This Mac Pro has a new install of OS 10.7.5, Lion, which is the latest it can run.
The case does have some scrapes and dings. Comes with power cable. I even have a Mac Pro box to ship it in!