Here it is, the second edition! Enjoy!
 
Xbox Live Marketplace
Deal of the Week - Blacklight: Tango Down - 50% off
Was 1200MP - Now 600MP
 
Steam
Square Enix Week - A new deal every day this week
PLUS the Square Enix Complete Pack (containing 31 games and plenty of DLC) - 87% off - Now £48.75/$74.99

Monday 14th - Batman: Arkham Asylum - 75% off - Now $7.50/£3.75 
Tuesday 15th - Just Cause franchise - 75% off - Now $3.75/£2.00 for Just Cause, and $7.50/£5.00 for Just Cause 2
Wednesday - Friday - I missed them :P
Saturday - 75% off all Kane and Lynch - including DLC : Now £3.74 for Kane and Lynch 2: Dog Days or £2.49 for Kane and Lynch: Dead Men
Sunday 20th - Tomb Raider Legend/ Anniversary/ Underworld - 75% off 
                           Lara Croft and the Guardian of Light - 66% off game and all DLC

Weekend Sale - 40% off Civilization V and 75% off all Civilization IV products. - Civ V now £17.99 - Civ IV Complete Edition now £3.75

Ongoing Sales - 
Portal 2 Preorders now on! - 10% off - Now $44.99/£26.99 (Includes a copy of Portal to own or gift)
Railworks Complete DLC Pack - Save $873 - Now $199.99/£149.99
The King's Crusade - 70% off - Now $9.00/£6.30
Witcher 2 Preorder - 10% off - Now $44.99 (US/Canada only)
 
Games For Windows Live Marketplace
Deal of the Week - (Changes every Thursday)
Street Fighter IV - 50% off - Now £9.99/$14.99 Until Thursday 17th

Direct2Drive
2K Week Deal of the Day - 14/02/11 - Civilization V  
25% off - Now $37.50/£22.45

Square Enix Week - 50% off all Square Enix/Eidos Titles - including:     (Doesn't seem available in the US store yet, I'll check back tomorrow)
Lara Croft and the Guardian of Light - £4.95
Front Mission Evolved - £14.95  
Kane and Lynch 1 - £6.25 
Kane and Lynch 2 - £9.95
Batman: Arkham Asylum Game of the Year - £9.95
Just Cause - £4.95
Just Cause 2 - £9.95
Mini Ninjas - £7.50
Battlestations: Pacific - £7.50
Shellshock 2: Blood Trails - £7.50
Tomb Raider Legend - £7.50
Tomb Raider Underworld - £7.50
Tomb Raider Anniversary - £6.25
Conflict: Denied Ops - £7.50
Infernal - £7.50
Battlestations: Midway - £4.95
Reservoir Dogs: The Game - £4.95 
Hitman 2: Silent Assassin - £4.95
Hitman: Blood Money - £4.95
Thief: Deadly Shadows - £3.75
Deus Ex - Game of the Year - £4.95
Deus Ex - Invisible War - £4.95