Although there are plenty of deals this weekend, there's probably not much you haven't seen before if you monitor game sales regularly, barring perhaps a 50% discount on Dark Souls: Prepare to Die Edition at Amazon as well as 33% off plus free weekend access to Counter-Strike: Global Offensive at Steam. Elsewhere, you'll find leftovers from last week's Halloween sales, particularly at GamersGate, and up to 75% off select military shooters at GameFly, space-themed games at Green Man Gaming and Assassin's Creed titles at Get Games (including an Assassin's Creed III preorder for $38.49).

Steam
85 Counter-Strike: Global Offensive $9.99 (33% off -- free weekend)
77  Killing Floor $4.99 (75% off)
78 Tomb Raider: Underworld $4.99 (75% off)
Tomb Raider: Anniversary $2.49 (75% off)
Tomb Raider: Legend $2.49 (75% off)
Defender's Quest: Valley of the Forgotten $9.99 (33% off)
Trains vs Zombies 2 $8.99 (50% off)
A Virus Named TOM $4.99 (50% off -- today only)
Tripwire Interactive Bundle $14.99 (75% off)
More...

Amazon Digital
81  The Walking Dead $14.99 (40% off)
93  Mass Effect 2 $7.00 (65% off)
75  Supreme Commander 2 $4.99 (67% off)
Dark Souls: Prepare to Die Edition $19.90 (50% off)
More...

GamersGate
83 Alan Wake $14.98 (50% off)
72 Penumbra Collection $5.00 (75% off)
70  NecroVision $3.89 (70% off)
61 NecroVision: Lost Company $5.99 (70% off)
79 Metro 2033 $4.99 (75% off)
72 F.E.A.R. Complete Pack $7.50 (75% off)
74 Dead Island $7.48 (50% off)
85 Amnesia: The Dark Descent $4.99 (75% off)
89 Dead Space Complete Pack $9.99 (75% off)
74 Dark Fall: Lost Souls $2.49 (75% off)
58 Alone in the Dark $2.49 (75% off) 
72  S.T.A.L.K.E.R. Clear Sky $2.49 (75% off)
80  S.T.A.L.K.E.R. Call of Pripyat $6.48 (50% off)
S.T.A.L.K.E.R. Shadow of Chernobyl $4.99 (75% off)
66-70% off Splinter Cell titles
More...

GameFly
71 Alice: Madness Returns $4.99 (75% off)
77 The Darkness II $7.49 (75% off)
66 Sniper Elite V2 $24.99 (50% off)
73 Spec Ops: The Line $14.99 (50% off)
77 Operation Flashpoint Dragon Rising $9.99 (75% off)
75 Ghost Recon: Future Soldier $23.99 (40% off)
74 Red Orchestra 2: Heroes of Stalingrad $9.99 (50% off)
72 Medal of Honor: Ultimate Digital Collection $11.99 (60% off)
50 Global Ops Commando Libya $7.49 (75% off)
Demigod $2.49 (75% off)
Vampire: The Masquerade - Bloodlines $4.99 (75% off)
Painkiller $1.25 (75% off)
More...

Green Man Gaming
73 Armada: Gold $7.99 (60% off)
58 Gemini Wars $15.99 (60% off)
84 Red Faction: Guerilla $4.99 (75% off)
71 Red Faction: Armageddon $4.99 (75% off)
77 Space Pirates and Zombies $3.73 (75% off)
75 Star Ruler $5.99 (60% off)
60 Starpoint Gemini $9.99 (60% off)
74 Unstoppable Gorg $2.49 (75% off)
79 Warhammer 40k: Dawn of War II - Retribution $7.49 (75% off)
85 Warhammer 40k: Dawn of War II - Chaos Rising $4.99 (75% off)
75 Warhammer 40k: Space Marine $7.49 (75% off)
88 Waveform $3.49 (50% off)
Earth 2160 $3.49 (50% off)
Galaxy on Fire 2 Full HD $9.99 (50% off)
J.U.L.I.A $9.99 (50% off)
Nexuiz $2.49 (75% off)
ORB: Off-World Resource Base $4.99 (50% off)
Red Faction $2.49 (75% off)
Rochard $4.99 (50% off)
SOL Exodus: Collector's Edition $5.99 (60% off)
Space Empires IV Deluxe $4.99 (50% off)
Space Empires: Starfury $4.99 (50% off)
Stellar Impact $4.99 (50% off)
Supreme Commander $4.99 (75% off)
UFO Extraterrestrials Gold Edition $3.73 $(75% off)
25% off most digital games via coupon code "GMG25-UAAHK-6AI9S"
More...

Get Games
90 Batman: Arkham Asylum GotY $4.99 (75% off)
90  Batman: Arkham City $9.99 (50% off)
84 Lego Batman $8.99 (55% off)
82 Lego Batman 2 $10.49 (65% off)
74 Lego Harry Potter: Years 1-4 $8.99 (55% off)
76 Lego Harry Potter: Years 5-7 $5.25 (65% off)
Far Cry Bundle $6.25 (75% off)
Up to 75% off Assassin's Creed titles (ACIII preorder for $38.49)
More...

GameStop
83  Saints Row: The Third $13.59 (66% off)
73  Blood Bowl Legendary Edition $19.99 (50% off)
More...

GOG
60% off many EA titles
30-40% off Deponia titles