This is in no specific order.  I will aslo be more than happy to change these if you give me a reason.  I did not put developers with only one good series unless it had an absolute reason.

EPIC GAMES

With the brilliant team at EPIC Games including Cliff Bleszinki and Rod Ferusson (Who are no longer with EPIC Games) they have made 1 hit game afeter another.  Not only that but they have changed the genre of TPS forever with Gears of War.  Gears of War was believed to be the 1st real new generation game for Xbox 360 and it definitely showed.  It would be one of the games that changed gaming for years to come.  Even Horde mode has been used for years brought by you know it, Gears of War.  I'm pretty sure you guys have heard of a little thing called Unreal Engine as well.

Games list

Jazz Jackrabbit
Age of Wonders
Unreal Tournament
Gears of War
Shadow Complex
Infinity Blade
Bulletstorm
(Upcoming game) Fortnite

Rockstar

These guys are brilliant as weel with blockbuster games like Grand Theft Auto and Red Dead Redemption.  In fact have they made a bad game this generation at all?  And just like Gears of War for EPIC Games we could say the same with Grand Theft Auto.  It gave us a new genre called sandbox.  One thing is for sure though, whether it is Grand Theft auto or Max Payne, we will pay attention if it has Rockstar on the cover.

Game List

Bully
Grand Theft Auto
Midnight Club
Manhunt
The Warriors
Red Dead Redemption
L.A. Noire
Max Payne
(Upcoming game) Agent

Blizzard

 Another company that can do no wrong.  In fact they have brought the insanley addicting World of Warcraft.  The game that seems it will never die.  This is the staple for MMO gaming.  Personally I have never played it, but regardless I have respect for a company that can do what it has with World of Warcraft.

Game List

World of Warcraft
Starcraft
Diablo
Warcraft



Valve

Valve you have brought us Halflife, Portal, hats, Glados, Gabe Newell, and Steam.  I can't say that their is a company that is more respected in the game industry from it's fans more than Valve fans.  I can't really blame them as Valve seems like 1 of the few game companies that are here to press forward on giving gamers good discounts and good games.  Still no Half-life 3 as of yet.....

Game list

Half-life
Team Fortress
Day of Defeat
Counterstrike
Gary's Mod
Portal
Left 4 Dead
Dota
(Upcoming Game 2033 release date) Half-life 3

Naughty Dog

A long with EPIC Games this is probably my personal favorite company.  I mean this company literally does no wrong.  Nothing they come out with is bad. Not a long list but I think the list will speak for its self.

Game List

Crash Bandicoot
Jak & Daxter
Uncharted
(Upcoming game) The Last of Us

Rare

The once golden child for Nintendo.  This company has so many articles about them it isn't even funny.  In fact people criticise them a lot now because of they think they have went down hill.  Honestly this is false.  They still make good games to this day.  The only difference is they are no longer revolutionary.  Maybe not as good as they once were but still a great company none the less. Let's look at the list

Game List

Blast Corps
Golden Eye
Diddy Kong Racing
Banjo Kazooie
Donkey Kong 64
Donkey Kong Country
Conkers Bad Fur Day
Star Fox
Killer Instict
Gabbed by the Ghoulies
Perfect Dark
Sabre Wulf
Kameo
Viva Pinata
Kinect Sports
(Upcoming Game Rumored) Rise NeXbox


Id Software

Id Software with John Carmack has been the pioneers of the game industry or at least the FPS genre.  If it wasn't for Id Software we could even argue that their would be no Valve or EPIC Games.  Now that is a big deal.

List of Games

Doom 
Wolfenstein
Rage
Quake
(Upcoming Game) Doom 4

Nintendo

What haven't they made that?

Game List

Metroid 
Donkey Kong 
Mario 
Zelda
Pikmin
Kid Icarus
Luigi's Mansion
And this list goes on and on


Bioware

I'm sure this will be a controversial decision but this may be the rising developer of this generation They have gained a lot of fans and well maybe lost a few but in the end they make great games with massive universes.  They have proven to be good early on and most likely will gain more respect in the coming years.

List of games

Baldur's Gate
MDK
Neverwinter Nights
Star Wars: Knights of the Old Republic
Jade Impact
Mass Effect 
Dragon Origin
(Upcoming Game) Dragon Age III

Bungie

Honestly their is only one reason to put Bungie on this list, and it is because they have reolutionized FPS and online gaming for consoles forever.  Without Halo it could be argued that FPS, Online Gaming, and XBOX 360 would not be here today so because of Halo Bungie has to be on this list.  

Game List

Marathon
Myth
Oni
Halo
(Upcoming Game) Destiny

For me, there are so few truly good developers left, there's mo point in making a top 10.

Arenanet is currently among the best though.

No Nintendo EAD?

Replace Retro with Nintendo and that makes for a good list.

I've only heard of three of those epic games... games.  Unreal, Gears and Bulletstorm.  Didn't know they developed Bulletstorm actually.  Hadn't heard of those other games until now.

Pretty good list anyway.  It's hard to argue with any of it.  They're all major established studios with a great history behind them and a great future in front of them.  The only one I'd question is Retro.  Don't get me wrong, I respect what they did with Metroid and DKCR with an enjoyable game.  I just feel like they're not... quite there yet. 

Anyway, if we're all making lists, mine would be:

Nintendo

Everything, really!

Bullfrog Productions

Populous; Theme Hospital; Dungeon Keeper.

Psygnosis (Studio Liverpool)

WipEout; Colony Wars; G-Police.

Insomniac Games

Spyro the Dragon; Ratchet & Clank; Resistance.

Naughty Dog

Crash Bandicoot; Jak & Daxter; Uncharted.

Maxis

SimCity; The Sims; Spore.

Squaresoft

Final Fantasy; Parasite Eve; Super Mario RPG.

Valve

Half Life; Team Fortress; Portal.

Rockstar

Grand Theft Auto; Canis Canem Edit; Red Dead Redemption.

Blizzard

Warcraft; Starcraft; Diablo.

Haha, this literally made me just realise that Blizzard only have 3 IP's.  Major IP's, but still.

Thanks i fixed it

Oh and just one other thing - I realise I've done it too, but there's a huge discrepancy between some of the studio sizes we've listed which makes it a bit unfair to compare.

For example, Square-Enix and Rockstar are both 10 different studios under one name (unless you listed them separately, such as "Rockstar North").

Comparatively, teams like Naughty Dog were just one studio until very recently, and Retro still is just one team I believe. It's harder for them to put out as varied and large a library as some of the other studios.

yeah, id software is bleh. 

Square Enix has like a gazillion different studios. Especially if you include A lot of old Eidos Defunct studios like Ion Storm. 

Nintendo isn't exactly one studio either as there's more than one EAD. If Eidos is going to be considered Square-Enix, then Retro should be considered with nintendo. Rare is debatable because Nintendo only owned 49% share when they were together.

Very true, but I suppose if we do that then everything just descends into posting publishers.  For example, if we were including Retro with Nintendo, then we'd have to include Naughty Dog with Sony, etc. etc.

I suppose there's got to be some cut off point though, because like you say, including both Eidos and Squeenix is ludicrous.