Along with free copies of Dragon Age: Origins and Bejeweled 3 on EA's platform, Borderlands 2 is only $5 at GameStop or $6.80 if you'd rather shop at GamersGate, which also lists Tomb Raider and Saints Row: The Third - The Full Package for $5 each, Hitman: Absolution for $6.25, Skyrim for $9.98 and Thief for $10.20. Also of note, the latest Humble Bundle includes both Darksiders releases alongside 10 other titles for $10 or whatever you're willing to part with.
Steam
75
Serious Sam Complete Pack $9.99 (90% off)
Naruto Shippuden: Ultimate Ninja Storm 3 Full Burst $9.99 (67% off)
83
Wargame Franchise Pack $20.00 (60% off)
76
Divinity Anthology $7.50 (75% off)
63
Contrast $3.74 (75% off)
72
Blood Bowl: Chaos Editon $7.49 (75% off)
Space Engineers $11.99 (40% off + free weekend access)
Kerbel Space Program $17.99 (40% off)
Race The Sun $2.49 (75% off)
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GameStop
87
Borderlands 2 $4.99 (75% off)
87
Borderlands 2 GotY $13.59 (66% off)
92
Company of Heroes $2.99 (66% off)
74
Cities in Motion 2 $4.99 (90% off)
85
Europa Universalis IV $9.99 (75% off)
38
Sword of the Stars II Enhanced Edition $4.99 (75% off)
78
Victoria II $4.99 (75% off)
78
Magicka $2.49 (75% off)
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GamersGate
87
Borderlands 2 $6.80 (66% off)
87
Borderlands 2 GotY $20.00 (50% off)
89
Tomb Raider $5.00 (75% off)
79
Hitman: Absolution $6.25 (75% off)
74
The Incredible Adventures of Van Helsing 1 Complete $5.00 (75% off)
85
Saints Row: The Third - The Full Package $5.00 (75% off)
94
TES V: Skyrim $9.98 (50% off)
94
TES V: Skyrim Legendary Edition $20.00 (50% off)
82
Just Cause 2 $3.75 (75% off -- DLC pack $1.75)
68
Thief $10.20 (66% off)
Legacy of Kain: Soul Reaver $1.50 (75% off)
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GameFly
87
Sid Meier's Civilization V Complete $19.99 (60% off)
88
Portal $2.49 (75% off)
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Green Man Gaming
84
Age of Empires III Complete Collection $9.99 (75% off)
FortressCraft Evolved $4.49 (50% off)
80% off Youda games
Up to 85% off Mastertronic games
20% off select titles via "OCTOBE-R20GMG-OFFERX"
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Get Games
65
Painkiller Hell and Damnation Collectors Edition $7.49 (75% off)
Blade Symphony $7.49 (50% off)
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Origin
90
Dragon Age: Origins $0.00 (free)
82
Bejewled 3 $0.00 (free)
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GOG
Pick three of these games and get up to 85% off