Stolen from CAG:

http://www.buy.com/prod/mad-catz-xbo...213824814.html

Buy.com has a Madcatz 360 wireless ethernet gaming adapter for a not ridiculous price. Select the economy shipping option and the shipping is free. It basically works as an ethernet bridge, so it isn't 360 specific and will work with any system with an ethernet port. Setting it up is slightly more challenging than an official MS adapter since you have to use a PC to configure it instead of the 360, but I wouldn't think most of the people here would have any trouble with it.