The sale starts on Tuesday 18th December through to the 31st. Discounts are yet to be revealed, so let this be a warning to not buy any of this stuff between now and then. 
Props to @lifelower.
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18th - 31st TWO WEEK SALE
XBLA Games
Frogger: Hyper Arcade Edition
Joe Danger 2: The Movie
Zuma's Revenge!
The Simpsons™ Arcade Game
Wreckateer
Plants vs. Zombies
Peggle
Peggle™ Nights Content Pack
Fire Pro Wrestling
SONIC 4 Episode II
Sonic The Hedgehog 2
RAW
A World of Keflings
A World of Keflings - Sugar, Spice and Not So Nice
A World of Keflings - It Came From Outer Space
Kinect Party
Jet Set Radio
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DAILY DEALS
18th: Modern Warfare 3
Modern Warfare® 3 [GoD]
Collection 1 DLC
Collection 2 DLC
Collection 3 DLC
Collection 4 DLC
19th: LEGO Games
LEGO Batman [GoD]
LEGO Star Wars: The Complete Saga [GoD]
LEGO Star Wars III [GoD]
LEGO® Indiana Jones™ [GoD]
LEGO Pirates of the Caribbean [GoD]
LEGO® Indiana Jones™ 2 [GoD]
LEGO® Harry Potter™ [GoD]
20th: Platformer Games
Fez
HELL YEAH! Wrath of the Dead Rabbit
Sonic Adventure™ 2
Rayman® Origins [ GoD]
Rayman 3 HD
Mark of the Ninja
Trine 2
21st: Rockstar Games
L.A. Noire [ GoD]
Red Dead Redemption [ GoD]
Max Payne 3 [ GoD]
Midnight Club: LA [ GoD]
22nd: TBA
23rd: Summer of Arcade 2012 Games
Dust: An Elysian Tail™
Deadlight
Hybrid
24th: Trials HD and Trials Evolution
Trials HD
Trials HD - Big Thrills
Trials HD - Big Pack
Trials Evolution
Trials Evolution: Origin of Pain
25th: Kinect Family
Hydro Thunder
Rock of Ages
Mini Ninjas Adventures
Leedmees
Fruit Ninja Kinect
Fruit Ninja Kinect - 8-bit Cartridge
Fruit Ninja Kinect - Art Box
Fruit Ninja Kinect - Space Capsule
Fruit Ninja Kinect - Storm Season
26th: TBA
27th: Borderlands
Borderlands [ GoD]
Borderlands 2 [ GoD]
Borderlands 2 Season Pass
28th: The Walking Dead
The Walking Dead Episode 1
The Walking Dead Episode 2
The Walking Dead Episode 3
The Walking Dead Episode 4
The Walking Dead Episode 5
29th: Family Games
Banjo Kazooie: Nuts & Bolts [ GoD]
Cars 2: The Video Game [ GoD]
Crash Of The Titans [ GoD]
Toy Story 3 [ GoD]
Crazy Taxi
The Splatters™
30th: Fighting Games
Virtua Fighter 5 Final Showdown
Street Fighter III: Online Edition
Dungeon Fighter LIVE: Fall Of Hendon Myre
31st: Skyrim and Oblivion
The Elder Scrolls V: Skyrim [ GoD]
The Elder Scrolls V: Skyrim: Dawnguard
The Elder Scrolls V: Skyrim: Hearthfire
The Elder Scrolls IV: Oblivion [ GoD]
The Elder Scrolls IV: Oblivion: Shivering Isles
The Elder Scrolls IV: Oblivion: Knights of the Nine