STEAM
It's a sequel hype-up weekend on Steam: Borderlands and its GOTY edition are both 75% off, as is Orcs Must Die! (There's also an Orcs Must Die! 2 demo available now, so have some of that.)
75% off Borderlands: Game of the Year - $7.49
75% off Orcs Must Die! Game of the Year - $3.24
82% off Civilization Collection - $24.99
66% off Ys The Oath in Felghana - $5.09
AMAZON
Amazon is running the same Borderlands deal as Steam, and many of the usuals are on sale as...usual.
75% off Borderlands Game of the Year Edition - $7.49
80% off Burning Hot Bundle - $7.99
72% off Mount & Blade - $4.17
50% off Mount & Blade: Warband - $10.03
61% off Dragon Age 2 - $7.81
25% off Mass Effect 2 - $14.92
71% off Trine - $5.83
50% off Mount & Blade: Warband - $9.95
27% off Dungeon Siege 3 - $14.68
52% off Tropico 4 - $19.17
26% off Command & Conquer: Red Alert 3 - $14.84
More Amazon PC game downloads
GAMEFLY
GameFly returns to the list this week with 50% off Max Payne 3 and 75% off Mirror's Edge. Nice!
50% off Max Payne 3 - $29.99
75% off Tom Clancy's Splinter Cell Conviction - $5.00
75% off Mirror's Edge - $5.00
50% off Nexuiz - $5.00
More GameFly deals
GAMESTOP
Bethesda games are up to 50% off this weekend on GameStop.
33% off The Elder Scrolls V: Skyrim - $40.19
50% off RAGE - $9.99
50% off Hunted: The Demon's Forge - $9.99
50% off The Elder Scrolls III: Morrowind GOTY Edition - $9.99
50% off The Elder Scrolls IV: Oblivion GOTY Deluxe Edition - $12.49
GOG
"Awesome Adventure Games" are 50% off on GOG this weekend. The list includes some personal favorites: The 11th Hour, Dreamfall: The Longest Journey, and Little Big Adventure (a.k.a Twinsen's Odyssey).
More game deals
Green Man Gaming's Summ...oh wait, Winter Sale
Update: I don't usually add pre-order deals, but it has come to my attention (thanks commenters!) that Green Man is offering Borderlands 2 pre-orders for $40 with the voucher: PARTP-ALCNO-TIESU.
If you find any great deals we missed, the comments are a lovely place to share them.