If you haven't already bought Max Payne 3, Green Man Gaming offers 20% off the digital download alongside 50-75% off Square Enix/Eidos titles including Deus Ex: Human Revolution, Just Cause 2, as well as the Tomb Raider, Thief and Hitman series (Blood Money is practically free at $2.48). You'll also find 75% off Cities XL 2012 at Steam, 75% off The Darkness II at Amazon, 33% off various Valve titles at GameStop, as well as solid deals on Mass Effect and Dead Space titles at GameFly.

Steam
74 Cities XL 2012 $10.00 (75% off)
82 Napoleon: Total War Imperial Edition $9.99 (50% off -- free to play this weekend)
Counter-Strike: Source $6.80 (66% off)
Nancy Drew: Secrets Can Kill $3.49 (50% off) 
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Amazon Digital
77 The Darkness II $12.49 (75% off)
90 FIFA Soccer 12 $9.99 (50% off)
74 Dead Island $11.99 (60% off)
87 Sid Meier's Civilization V $14.99 (50% off)
80 Risen $5.99 (70% off)
88 Battlefield 3 $36.99 (38% off)
79 Mount & Blade: Warband $9.94 (50% off)
69 Payday: The Heist $9.99 (50% off)
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GameStop
86  Mass Effect 3 $39.99 (33% off)
95  Portal 2 $20.09 (33% off)
88  Left 4 Dead $13.39 (33% off)
88 Left 4 Dead 2 $13.39 (33% off)
88 Half-Life 2: Orange Box $13.39 (33% off)
82 Darksiders $4.99 (75% off)
74 Assassin's Creed $4.99 (75% off)
89 Assassin's Creed 2 $9.99 (50% off)
87 Assassin's Creed: Brotherhood $14.99 (50% off)
86 BioShock $9.99 (50% off)
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GamersGate
74  Dead Island $11.98 (60% off)
88 Football Manager 2012 $10.18 (66% off)
90 FIFA Soccer 12 $11.97 (40% off)
78  Might & Magic Heroes VI $24.98 (50% off)
Heroes of Might & Magic V $2.99 (70% off)
Might & Magic: Clash of Heroes $7.48 (50% off)
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GameFly
75 Warhammer 40,000: Space Marine $10.19 (66% off)
93 Mass Effect 2 $4.99 (75% off)
86  Mass Effect 3 $35.99 (40% off)
87  Dead Space $4.99 (75% off)
89 Dead Space 2 $4.99 (75% off)
Space Quest Collection $4.99 (75% off)
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Green Man Gaming
84 Max Payne 3 $47.99 (20% off)
87 Deus Ex: Human Revolution $7.50 (75% off) 
67 Dungeon Siege III $9.99 (50% off)
82 Just Cause 2 $7.50 (74% off)
68 Kane and Lynch 2: Dog Days $10.00 (49% off)
78  Tomb Raider: Underworld $15.00 (49% off)
82  Lara Croft and the Guardian of Light $7.49 (50% off)
Tomb Raider Anniversary $4.98 (49% off)
Tomb Raider: Legend $9.98 (49% off)
Thief Gold $4.99 (50% off)
Thief II: The Metal Age $4.99 (50% off)
Thief: Deadly Shadows $4.99 (75% off)
Hitman 2: Silent Assassin $4.98 (49% off)
Hitman: Blood Money $2.48 (75% off)
Just Cause $7.48 (49% off)
Scarygirl $5.00 (49% off)
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Origin
Up to 40% off select Special Edition titles
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GOG
50% off select Ubisoft titles