I had an email in my inbox this afternoon with three Xbox LIVE marketplace codes to download games -- Joust, Frogger, and Robotron. The letter said they're sending them out to anyone who bought their 360 in the calendar year and registered it on xbox.com.
I have no idea if it will still work, but if you haven't registered your console yet, I figured you might want to give it a shot and see if you'll get one of these emails, too. Three free games for a simple form seems more than worth the hassle.
Also, did anyone else get any different games? Or does everyone get the same ones?