MegaMacs offers the refurbished Apple iMac Core i5 2.5GHz 21.5" Desktop, model no. MC812LL/A, for $649.99 plus $32.33 for shipping. That's $77 below our mention of a refurb from a month ago (which featured a slightly faster processor) and $142 under the lowest total price we could find for a refurb now. It features an Intel Core i5 2.5GHz quad-core processor, 21.5" 1920x1080 (1080p) LCD, 4GB RAM, 1TB hard drive, DVD burner, Airport card (802.11n wireless), Bluetooth, and OSX 10.9 (Mavericks). Deal ends April 22.
Note that the mouse and keyboard, pictured, are not included. A 30-day MegaMacs warranty applies.