If you've missed the few other chances to grab Borderlands 2 at half off since September, Steam offers another opportunity this weekend, pricing the game at $29.99 for one license or $89.99 for four ($22.49 each). You'll also find Counter-Strike: Global Offensive for $7.49 on Valve's service, a C&C collection for $16.99 via Amazon, Deus Ex: Human Revolution for $5 at GamersGate, up to 80% off Crysis and Dragon Age titles at GameFly, as well as 75% off Batman: Arkham City GotY, both Darksiders games, various Lego titles and the F.E.A.R. series at Get Games.

Steam
88 Borderlands 2 $29.99 (50% off)
83 Borderlands GotY $7.49 (75% off)
85 Counter-Strike: Global Offensive $7.49 (50% off)
85 Counter-Strike Complete $14.99 (50% off)
73 Cities in Motion Collection $12.49 (75% off)
67 Test Drive Unlimited 2 $4.99 (75% off -- today only)
More...

Amazon Digital
68 Command & Conquer The Ultimate Collection $16.99 (43% off)
68 Dungeon Siege Bundle $11.99 (87% off)
More...

GameStop
86 Dawn of Discovery Gold $9.99 (50% off)
80 The Settlers 7: Paths to a Kingdom $6.59 (67% off)
79 R.U.S.E. $9.99 (50% off)
68 H.A.W.X. 2 $9.99 (50% off)
74 Sengoku $9.99 (50% off)
64  Pirates of Black Cove $9.99 (50% off)
Sine Mora $4.99 (50% off)
I Am Alive $7.49 (50% off)
More...

GamersGate
87 Deus Ex: Human Revolution $5.00 (75% off)
87 Deus Ex: Collection $11.25 (75% off)
59 Defenders of Ardania Collection $6.50 (50% off) 
74  Majesty 2 Collection $9.98 (50% off)
Majesty Collection $39.98 (50% off)
Stealth Bastard Deluxe $5.00 (50% off)
More...

GameFly
90 Dragon Age: Origins Ultimate Collection $7.49 (75% off)
79 Dragon Age II $4.99 (50% off)
90 Dragon Age Bundle $9.99 (80% off)
88  Crysis Maximum Edition $7.49 (75% off)
86 Crysis 2 Maximum Edition $9.99 (75% off)
88 Crysis Collection $13.99 (80% off)
More...

Green Man Gaming
78 Dear Esther $1.38 (75% off)
60  Avencast: Rise of the Mage $2.48 (75% off)
60  Bus Driver $2.49 (75% off)
66  Grotesque Tactics 2 $2.49 (75% off)
50  P.A.M. $2.49 (75% off)
88  Waveform $1.74 (75% off)
Miner Wars 2081 (50% off)
Miner Wars MMO $4.99 (50% off)
Wasteland Angel $2.49 (75% off)
25% off preorders via "GMG25-T6JV8-1NPBA"
More...

Get Games 
90 Batman: Arkham City GotY $7.49 (75% off)
82 Darksiders $7.49 (75% off)
78 Darksiders II $12.49 (75% off)
77 Lego Batman $4.99 (75% off)
84 Lego Batman 2 $7.49 (75% off)
82 Lego Lord of the Rings $10.19 (66% off)
74 Lego Harry Potter: Years 1-4 $4.99 (75% off)
76 Lego Harry Potter: Years 5-7 $3.74 (75% off)
88 F.E.A.R. $3.74 (75% off)
78  F.E.A.R. 2 $3.74 (75% off)
72  F.E.A.R. 3 $9.99 (75% off)
Sega Sci-Fi Pack $18.74 (75% off)
The Trouble With Robots $3.99 (60% off)
More...

GOG
50% off Square Enix titles