If you've been meaning to catch up on the Assassin's Creed franchise before the next entry arrives in November, GamersGate has 60-83% off the first four titles. Also of note, for the next ~11 hours (or until supplies run out), G2Play offers Assassin's Creed III for only $36.48, the cheapest preorder deal we've seen. Other noteworthy deals include half off Sleeping Dogs and The Witcher at Steam, up to 75% off assorted EA and Paradox titles at GameFly, and savings on horror-themed games at Green Man Gaming.

Steam
80 Sleeping Dogs $24.99 (50% off)
69 Payday: The Heist $4.99 (75% off)
81 The Witcher: Enhanced Edition $4.99 (50% off)
71  Choplifter HD $2.49 (75% off)
64  Alpha Protocol $4.99 (75% off -- today only)
The Bard's Tale $2.49 (75% off)
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Amazon Digital
78 Endless Space Emperor Special Edition $23.44 
93 Mass Effect 2 $9.94 (50% off)
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GameStop
93  TES V: Skyrim $35.99 (40% off)
61 Lost Planet 2 $9.99 (50% off)
Lost Planet Extreme Condition $9.99 (50% off)
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GamersGate
79 Assassin's Creed: Revelations $11.98 (60% off)
88 Assassin's Creed: Brotherhood $4.99 (83% off)
89  Assassin's Creed 2 Deluxe $4.99 (75% off)
74 Assassin's Creed $4.99 ((75% off)
80 AI War Pack $5.98 (75% off)
Aces High $7.49 (75% off)
Air Conflicts - Secret Wars $9.98 (50% off)
Wings of Honour $1.25 (75% off)
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GameFly
86  Crysis 2 Maximum Edition $9.99 (75% off)
81  Kingdoms of Amalur: Reckoning $15.99 (60% off)
87  Mass Effect 3 $14.99 (50% off)
88  Battlefield 3 $19.99 (50% off)
63  Darkspore $4.99 (75% off)
81  Command and Conquer Red Alert 3 $4.99 (75% off)
78  Dragon Age II $4.99 (75% off)
89  Dead Space 2 $4.99 (75% off)
79  Mirror's Edge $4.99 (75% off)
79 Mount and Blade: Warband $4.99 (75% off)
73 Warlock: Master of the Arcane $4.99 (75% off)
75 Magicka Collection $6.25 (75% off)
76 Hearts of Iron III Collection $7.49 (75% off)
73 Cities in Motion $4.99 (75% off)
66 King Arthur Collection $6.25 (75% off)
SimCity 4 Deluxe Edition $4.99 (75% off)
Europa Universalis III Chronicles $7.49 (75% off)
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Green Man Gaming 
75 Dead Island GotY $9.99 (50% off)
78 Darksiders II $24.99 (50% off)
82  Darksiders $4.99 (75% off)
77 The Darkness II $7.49 (75% off)
83 Alan Wake: Collector's Edition $17.47 (50% off)
65 Darkness Within 2 $4.99 (50% off)
77 Killing Floor $9.99 (50% off)
72 F.E.A.R. 3 $9.99 (50% off)
35 Postal III $14.99 (50% off)
69  Risen 2: Dark Waters $16.99 (66% off)
79  Metro 2033 $4.98 (75% off)
74  Dark Fall: Lost Souls $4.99 (50% off)
66  Alter Ego $7.49 (50% off)
56  Trapped Dead $2.48 (75% off)
47  Painkiller Resurrection $2.49 (75% off)
86  BioShock 2 $9.99 (50% off)
BioShock $9.99 (50% off)
Painkiller Black Edition $2.48 (75% off)
Painkiller Recurring Evil $2.49 (75% off)
Painkiller Overdose $1.24 (75% off)
Dark Fall: Lights Out $4.99 (50% off)
The Rockin' Dead $3.49 (65% off)
Three Dead Zed $2.49 (50% off)
All Zombies Must Die! $3.99 (60% off)
Condemned $7.49 (50% off)
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Get Games
82 Dungeon Siege III $4.99 (75% off)
78  Overlord II $2.49 (75% off)
76  Men of War Gold/Assault Bundle $12.49 (75% off)
78  Heroes of Might & Magic VI Gold $19.99 (50% off)
67 Arcania - Gothic 4 $4.99 (75% off)
53  Gothic 3 Enhanced Edition $2.49 (75% off)
Gothic II Gold $2.49 (75% off)
Blades of Time Limited Edition $17.99 (60% off)
Heroes of Might & Magic V $3.89 (70% off)
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GOG 
Pay what you want for Interplay titles
50% off "Mac & PC Essentials"
30-40% off Deponia titles