Steam has slashed up to 50% off 2K Games' catalog, with a special daily deal on Mafia and Mafia II (75% off). The weekend-long promotion ends Sunday with extra savings on a new game every day. There's not a whole lot happening elsewhere, though Deus Ex: Human Revolution is on sale again, this time via GamersGate for a measly $7.49 ($9.99 for the Augmented Edition). GameStop offers 33% off Skyrim, while Microsoft shaves a few bucks off Batman: Arkham City.

Steam
83 Borderlands GotY $14.99 (50% off)
87 Civilization V GotY $24.99 (50% off) 
82 Mafia II $7.49 (75% off)
77 The Darkness II $37.49 (25% off)
44 The Stronghold Collection $9.99 (50% off)
91 NBA 2K12 $14.99 (50% off)
73  Hector: Badge of Carnage Full Series $4.99 (75% off -- today only)
86  BioShock 2 $9.99 (50% off)
BioShock $9.99 (50% off)
Double Fine Bundle $19.99 (33% off)
Stacking $9.99 (33% off)
X-COM: Complete Pack $7.49 (50% off)
Psychonauts $4.99 (50% off)
Axel & Pixel $2.49 (50% off)
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Amazon Digital
88 Football Manager 2012 $5.99 (85% off)
80 Divinity II: The Dragon Knight Saga $5.99 (85% off)
69 Payday: The Heist $7.49 (63% off)
65 Cities XL 2012 $9.99 (75% off)
74 Dead Island $14.99 (50% off)
71 Red Faction: Armageddon $15.11 (24% off)
75 Warhammer 40,000: Space Marine $23.46 (22% off)
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GameStop
88 Fallout 3 $9.99 (50% off)
93 TES V: Skyrim $39.99 (33% off)
88 CoD: Modern Warfare 2 $9.99 (50% off)
81 C&C: Red Alert 3 $6.99 (65% off)
68 C&C 4: Tiberian Twilight $6.99 (65% off)
74 Brink $9.99 (50% off)
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GamersGate
87 Deus Ex: Human Revolution $7.49 (75% off) 
87 Deus Ex: Human Revolution Augmented Edition $9.99 (75% off)
Deus Ex: GotY $2.50 (75% off)
Deus Ex: Invisible War $2.50 (75% off)
Evochron Mercenary $17.47 (30% off)
Sword of the Stars Complete Collection $5.99 (70% off)
Sword of the Stars II: Lord of Winter $8.99 (70% off)
Majesty 2 Collection $4.99 (75% off)
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GameFly
87 Dead Space $2.99 (70% off)
90 FIFA Soccer 12 $19.99 (50% off)

Games for Windows
89 Batman: Arkham City $37.49 (25% off)

Good Old Games
50% off 10 Activision games