I'm not good with subdivisions inside developers. For me Blizzard Entertainment is the whole of Blizzard (Diablo, StarCraft, WarCraft and Overwatch) and Nintendo is 2D Mario, 3D Mario, Smash, Mario Kart, Zelda, Metroid, Kirby, etc.) I know it's not the same studio that does it all but I never bothered to learn which does what.

Nintendo's Zelda Team

MONOLITH Soft

From Software

Square Enix (not as much as in the past though)

Santa Monica

Gurilla Games

CDPR

Panic Button

Bethesda

Monolith Soft has become a favourite of recent years, based off of Xenoblade Chronicles X, 2, and Torna alone.

I can't wait to see what they put out next :)

Yeah it was 2 and Torna that won't me over.  I have X for the WiiU still in the plastic, which I WILL get to when I get the chance.

X is amazing. The only complaint I have for it was the level cap at 60, but whatever. 

I never played the first one. I hope they bring an HD version to Switch.

Valve doesn't make games, anymore, so they should be excluded right off the bat.

I've seen most of the other studios I would name listed in other posts, so I won't bother in that regard.  But, one of my all-time favorites is the PC developer of the grand strategy games Europa Universalis, Hearts of Iron, Crusader Kings, and Victoria:

Paradox Development Studio

Pretty much everything I like is represented here, so here's one from my childhood.
The learning company- Treasure Mountain, the best game to learn math.

You mean a trading card game? That doesn't count, lol. The fans' E3 reaction should tell you everything you need to know.

So a trading card GAME, isnt a game anymore? Its by objective definition, a game, regardless of if youre interested or not.