Depends on your gametaste. I bet their are people out their who thinks Miyamoto contributed more than the rest of the planet.

JAPAN! over 80% of my library is japanese (L)

Japan der :) O.o Nintendo and Sony anyone?

For gaming as a whole?
US
Japan
Everything else together

For the games I like to play?
Japan
US
Everything else together

I say in historical terms but in revenue currently it is America.

I say
1. Japan- universally known but in current gen not
1*. Russia-TETRIS!!!!!!!!!!!
2. America- this includes USA and Canada.
3. UK is great for stragedy lovers. Until this country releases their own console they will never be number 1
4. France- Ubisoft

Their HQ is in California, but they have large devs in Canada.

I'm surprised how many people are ruling out PC gaming here... I know that as a method of profit it currently isn't as great as it could be, but I believe developers and publishers will begin to capitalize again on it in the future.. anyway, without further ado..

id software for Doom, pretty much the most revolutionary shooter ever created.
3d Realms for Duke Nukem.. the reason you have games like gears of war today.
Black Isle Studios: Kings of RPGs, no one has ever matched them.. along with
BioWare: Baldur's Gate?
Looking Glass Studios: System shock 2, ultima
Will Wright and co: Spore, The Sims
Blizzard Entertainment: Diablo, Starcraft, Warcraft, World of Warcraft
Valve
Bethesda
Maxis
Rockstar got their fame on PCs..
Remedy For Max Payne
Eidos for Deus Ex


In fact, for those who mention things like Tetris and jRPGs..

North Americans are responsible for tetris and japanese rpgs.
well, one north american.

Henk Rogers. He brough tetris to consoles (its not a japanese game) and he also created
"The Black Onyx" The very first Japanese RPG.

Henk Rogers.. From Bullet-Proof Software

japan.... and japan.

Oh, also japan. And lets not forget japan.

Oh, and did i mention japan?? x)

Well, Japan and the US i guess

Lot of different countries can develop blockbuster games if they have the will and an idea to make it happen. :)

but overally the most games (good & bad) are released by Japan, USA and UK propably. Can't forget Canada too since they got bioware. :O

Brazil.... joking

1. Japan
.
2 USA
.
.
.
.
3 Others