If picking up an xbox One at a Game midnight launch I hear the following offers will be on:
Fighter Within half price £25
LEGO Marvel Super Heroes half price £25 (game has been delayed but i hear will be honoured)
Call of Duty: Ghosts for £40 (or free if you trade in a current-gen version of Ghosts previously purchased at GAME)
£10 off a number of games (Forza Motorsport 5, Dead Rising 3, Ryse: Son of Rome, FIFA 14, Battlefield 4, Need For Speed: Rivals, NBA 2K14, Madden NFL 25)
£10 off a 12 Month Xbox LIVE Day One Edition Subscription.
Reduced price BluRays (£12.99 each: The Wolverine, Man Of Steel, Despicable Me 2, Kick-Ass 2, Alan Partridge: Alpha Papa, Pacific Rim.)
Possibly other deals. I'm not sure whether these deals are set in stone or just rumour but I've seen mention in a couple of places.