Absolutely. I was livid with Microsoft when they announced the closure of these studios too.

I wonder if they would have made the same choice considering their investment in studios now?

Off the top of my head:

EA Black Box (Need for Speed: Most Wanted 2005, Skate 2)
Westwood (Command & Conquer)
Core Design (Tomb Raider)

Cing

- Hotel Dusk
- Last Window

- Another Code
- Another Code R

- Little King's Story

Pheww, that's gonna be a long list. Let's see...

- Bullfrog (Theme Park, Dungeon Keeper, Magic Carpet, Populous,...)

- Sir-Tech (Wizardry, Jagged Alliance)

- Lionhead Studios (Black & White)

- New World Computing (Might & Magic)

- Black Isle Studio (Fallout, Baldur's Gate, Icewind Dale, Planetscape Torment)

- Origin Systems (Ultima, Wing Commander)

- Sierra On-Line (Leisure Suit Larry, Caesar, Earthsiege/Starsiege, 3D Ultra Pinball, Lords of the Realm/Magic,...) 

- Interplay (Fatal Racing (aka Whiplash), MDK, Descent)

- Blizzard Entertainment (Warcraft, Starcraft, Diablo)

- Westwood Studios (Command & Conquer, Lands of Lore, Dune, Eye of the Beholder)

- Maxis ( Sim City, Sim Tower, Sim...)

- Lucasfilm Games (Monkey Island, Indiana Jones, Afterlife)

There are more, but that's just from the top of my head now

- Looking Glass Studios (Thief I&II)

- Ion Storm (Deus Ex)

- EA Sports BIG (the SSX series)

Main one is Psygnosis. They gave us Wipeout, G-Police, Colony Wars and Rollcage, among other games as devs and published loads more.

Some good names there

Freelancer and B&W2 were couple of my favourite games of all time. I always wanted a Star Fox to grow into a cross between Star Fox Adventures and Freelander lol.

Sierra was also mentioned, loved that they got Starseige Tribes out and allowed the community to create mods for it.

Psygnosis, Bullfrog, Westwood, Sierra, among others.

I would also add Bioware and Blizzard, simply because they're dead to me in their current state.

Red Company (Sakura Wars, Far East of Eden, Thousand Arms)

Human Entertainment (Clock Tower)

Working Designs. Yes, they're a publisher and not a developer, and people nowadays criticize their localizations with the Clinton and M&M jokes and the "tweaks" to the gameplay that made some of the games unnecessarily difficult, but damn, did they bring us some good games.

Data East (Bad Dudes, Chelnov, Karnov, Midnight Resistance, a lot of pinball machines)

I miss a lot of the old Enix studios. Quintet (ActRaiser, SoulBlazer, Illusion of Gaia, Terranigma, Granstream Saga), Produce! (7th Saga, Brain Lord), Givro (Wonder Project).

Also haven't heard anything from Treasure in over ten years, so safe to assume they're gone.

I thought of another one: Flagship Studios, which handled the Nintendo/Capcom Zelda games and some of the stuff in Resident Evil.