GOG.com only:
Inquisitor
Urban Chaos
Blood Omen
Uplink
Deponia
A New Beginning
The Dark Eye: Chains of Satinav
Edna & Harvey
To The Moon
Stacking
The Real Texas
Divinity II
MOHAA Warchest
Symphony
8 gift codes

Additionally:
Spycraft
Shadow Warrior
The Journeyman Project 3
The 11th Hour
Darkstone
Bioforge
Battle Realms + Winter of the Wolf
Sratches
Runaway
Runaway 2
Lucius
KKnD Xtreme

That still leaves 6 games on my wishlist.
5 don''t have a promo and the 6th is only 33% off.

I'm not sure which date exactly I'm supposed to start from, but if I start from e.g. Dec 12 when GOG launched its "Holiday Gift Duke Nukem 3D":

GOG:

Duke Nukem 3D Atomic Edition (freebie)
ArmA 2
Inquisitor
The Real Texas
Gangsters: Organized Crime
Legacy of Kain: Blood Omen 2
Startopia
Urban Chaos
Spacechem
Anomaly Warzone Earth
Defender's Quest
Deponia
A New Beginning - Final Cut
Dark Eye: The Chains of Satinav
Edna & Harvey: The Breakout + Harvey's New Eyes
Stacking
Capsized
La Mulana
Snapshot
Giana Sisters: Twisted Dreams
Symphony
The Ball
Incredipede
Puddle
Unmechanical
Medal of Honor: Allied Assault War Chest
Moonbase Commander
Star Control 1+2
Fragile Allegiance
Divinity 2: Developer's Cut
Dungeon Keeper
Populous
Magic Carpet
Populous 2: Trials of the Olympian Gods
Syndicate
Populous: The Beginning
Sid Meier's Alpha Centauri

And I have still some remaining GOG items I intend to buy before the end of the year.

Humble Indie Bundle 7:

Dungeon Defenders + DLC
Legend of Grimrock
Snapshot
The Binding of Isaac + Wrath of the Lamb
Closure
(Indie Game: The Movie)
Shank 2

GetGamesGo:

Spec Ops: The Line (Steam)

Steam:

Mirror's Edge
Saints Row 2
Saints Row The Third: The Full Package
Half-Life 2: Episode One
Half-Life 2: Episode Two

Bioshock Dual Pack
Magicka: Grimnir's Laboratory

From Gog : LOK : Soulreaver; Startopia;
From Amazon : Lego LOTR; THQ Medley Bundle; Darksiders II Bundle;
From GG : Cargo Commander, Botanicula

Not sure will be getting much more - sitting on fence about Awesomenauts/or its soundtrack & a few other Gog games,,

Kingdom of Amalur Collection (£8.99)
Bethesda New Year Collection (£18.99)

I just bought a few more games from GOG during this sale. Don't expect to buy anything more right now. I'm actually not even looking at other digital retailers since with my hardly-ever-decreasing backlog there's not much sense in it. Plenty of stuff to keep me entertained around these parts, especially since the majority of it runs superbly on my crappy lappie. Yay, old(ish) games!

Anywho, this is what I've bought since the sale started:
Urban Chaos
Tomb Raider: Last Revelation/Chronicles
Tomb Raider: Angel of Darkness
Stacking (which unfortunately chugs a little too much on my lappie to be enjoyable enough)
A New Beginning (already completed ;))
Hostile Waters: Antaeus Rising
The Dark Eye: Chains of Satinav

I probably would have bought more if a certain Secret Santa hadn't surprisingly bought something like half my wishlist for me, so that was nice. I actually ended up spending more on others than myself this year, to the tune of seventy-some bucks.

Just starting from 20th December:

Google Play: Need for Speed Most Wanted, Wild Blood
GamersGate: Gray Matter
Amazon: LEGO LotR
Xbox LIve Arcade: Leedmess, Rock of Ages

GOG games I bought this holiday:
-Heroes Chronicles
-FTL
-Shadow Warrior Complete

Steam games I bought:
-Humble Indie Bundle, mostly for Shank 2 and Snapshot

GOG games I received from a giveaway:
-Hotline Miami (thanks again gracious lukew)

Steam games I received from a giveaway:
-Deadlight (ne_zavarj's humongous giveaway)
-Warhammer 40k Dawn of War (ninja'ed this one)

And naturally, the Duke Nukem 3D Holiday gift, although I already had it on the Xbox 360.

One last purchase I'm considering is Nation Red from Steam; it doesn't cost a lot but I may need to consider every single purchase in 2013 more thoroughly since I might become jobless in March in the worst case scenario - my contract is extended by only two months at the moment (plus it's only part-time) and a future project is still short of funding; I'm keeping my thumbs up though (sorry for a bit of off-topic).

Out of the ones I've gotten, I've so far played through Hotline Miami (man was it awesome, if a tad short), and the first four chapters of Heroes Chronicles. After I finish the rest of the chapters, I'm moving on to Shadow Warrior.

Humble Indie Bundle 7

2x Torchlight II on Steam.

GOG.com

The Witcher 2
FTL
Ultima VII
Ultima VIII
Ultima IX
Ultima Underworld 1 + 2
The Chronicles of Riddick Assault on Dark Athena
Painkiller Black Edition

Amazon.com
S.T.A.L.K.E.R. Shadow of Chernobyl
Leisure Suit Larry Collection
Army Men Warchest
Myth Total Codex
Neverwinter Nights Collection
Rome Total War Anthology
Starcraft Battlechest

Humble Bundle 7

Local
Diablo 2 Battlechest
Command and Conquer First Decade

Starcraft and Diablo 2 were replacements as my discs were shot. Also looking to try somethings I missed when they first came out. Myth II Soulblighter being one.

GOG:
2 games for the Secret Santa
Copy of Arcanum for my fr34ksh0w g1v34w4y.
Indirectly a copy of Alpha Centauri.

Steam:
2 copies of Arkham City (one for me, one for my friend)
KotOR2- for someone else, received Alpha Centauri in trade.
Drakensang series- for someone else. Received Borderlands 2 Season Pass in trade.

The Whispered World
Darksiders franchise pack (Amazon)
Saints Row the Third bundle (Steam)
Binary Domain (Green Man Gaming)

Surprisingly few games this holiday season, although I've been tempted by a few others, am tempted by a couple at the time of this posting, and I'm sure I'll be tempted by yet more in the coming days. Still, I've shown remarkable restraint thus far, I tihnk.

*edit* Oh, and I picked up 5 games for the Secret Santa giveaway here on GOG, but I'm not sure if I should count those.

KQ 1-3
KQ 4-6
Broken Sword 4
Apache Longbow
Broken Sword 2
Screamer 2
Bioforge
Terminal Velocity
KKND
Spycraft
Hind
King of Dragon Pass

My wishlist is EMPTY atm - have to do sth about it soon :-P

...

La Mulana
FTL
Beyond Good and Evil
Two Worlds
Tom Clancy's Splinter Cell
Tomb Raider: The Last Revelation + Chronicles
Psychonauts
MDK
MDK 2

Also considering buying some indie games from Steam, but I'm not sure...
Oh yeah, I've bought Bientôt l'été from Tale of Tales.