CowBoom offers the used Microsoft Xbox 360 E 250GB Console, model no. M9V-00001, for $99.99 with free shipping. That's $90 below our Thanksgiving mention of a new unit, which also included four games, and the lowest total price we've seen. (It's a current low by $150 for a refurb.) It features 250GB internal memory, WiFi, and a wireless controller.
Note: No warranty information is provided. This used unit may be missing parts or accessories and have dents or scratches.