I was looking for possible savings on (savings on most of these would need to be in the 50% off range)...
* Kinect Sports Rivals,
* ScreamRide (won't happen because they introduced a bundle with Zoo Tycoon),
* The Wolf Among Us (Xbox One),
* Fallout 4 (I know 33% off at most - $40ish and I would probably get it),
* Overlord Fellowship of Evil
* Shovel Knight.
* A few LEGO games if they were cheap enough (360)
* South Park: The Stick of Truth (though I hate the abortion mini game)
* Torchlight
I will not buy "arcade" games for $20, I am not really a fan of $15 either. So far not so good. I have only picked up Forza Horizon 2 DLC Storm Island and Kings Quest Episode 1 (because it was $1.50, $0.99 on the 360).
For a list of stuff on sale look at the link below (if it decides to be linky, if not, copy and paste).
http://majornelson.com/2015/12/21/the-official-list-of-deals-on-xbox-stores-countdown-the-biggest-sale-ever/