Digital distributors are embracing the Halloween spirit with huge savings on horror-themed titles. Although Steam seems to have the largest selection, many of the major games such as Dead Space, Dead Island, Killing Floor, Amnesia: The Dark Descent and others are available through most of Valve's competitors. However, we tried to avoid repeating those entries to keep the list as diverse as possible. As a side note, there is an event similar to the Humble Indie Bundle running over at Indie Royale.

Steam
89 Dead Space Pack $13.59 (66% off)
88 Left 4 Dead 2 $6.79 (66% off)
83 Borderlands: GotY $7.49 (75% off)
86 BioShock & BioShock 2 $4.99 (75% off)
75 Dead Island $37.49 (25% off)
77 Killing Floor Bundle $10.17 (66% off)
80 S.T.A.L.K.E.R. Bundle $8.74 (75% off)
47 Painkiller Complete Pack $10.17 (66% off)
85 Amnesia: The Dark Descent $4.00 (80% off)
78 Overlord Complete Pack $4.99 (75% off)
84 Resident Evil 5 $9.99 (50% off)
78 F.E.A.R. Collection $6.79
72  F.E.A.R. 3 $29.99 (40% off)
85 Terraria $4.99 (50% off)
76 Ghostbusters: The Video Game $2.49 (75% off)
81 Devil May Cry 4 $9.99 (50% off)
64 Silent Hill Homecoming $13.59 (66% off)
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Impulse
79 Metro 2033 $9.99 (50% off -- Fri. only)
68 Command and Conquer 4 $9.99 (50% off -- Sat. only)
79 Mirror's Edge $9.99 (50% off - Sun. only)
71 Alice: Madness Returns $14.99 (50% off)
84 Rift $9.99 (66% off)
46 Ghostbusters: Sanctum of Slime $4.99 (50% off)
56 Trapped Dead $4.99 (50% off)
Sword of the Stars Complete Collection $8.99 (55% off)
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GamersGate
67 Aliens vs. Predator $6.78 (83% off)
90 Batman: Arkham Asylum GotY $6.79 (66% off)
84 Lego Batman: The Video Game $6.78 (66% off)
60 Cryostatis: Sleep of Reason $4.40 (66% off)
74 Dark Fall: Lost Souls $6.66 (67% off)
72 Penumbra Collection $5.00 (75% off)
70 NecroVision Hardcore Edition $8.48 (66% off)
64 Disciples III: Renaissance $7.49 (75% off)
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Direct2Drive 
78 Call of Juarez: Bound in Blood $4.95 (75% off)
74 Hard Reset $14.95 (50% off)
88 Assassin's Creed: Brotherhood $19.95 (50% off)
82 Total War Deluxe $44.95 (50% off)
Fort Zombie $2.50 (75% off)
Haunted House $4.95 (75% off)
Fishdom: Spooky Splash $1.75 (75% off)
Vampire: The Masquerade - Bloodlines $4.95 (75% off)
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Origin
SimCity 4 Deluxe Edition $9.99 (50% off)

Good Old Games 
50% off "Spooky" games