Rare and Rockstar are defo 2 companies that i have a lot of time for.

Perfect dark, Banjo and Goldeneye are excellent.

GTA, Bully and Manhunt are fantastic.

Level - 5
Team Ico
Square Enix (tho i hate them for being so stupid lately and not releasing games on the console i own, and the fact that they're releasing crappy games on xbox360!)

Cant say Kojima Productions cause i only played the Metal Gear Series, cant say Sony cause that would make me sound like a fanboy (tho i really like them as a whole since i love Naughty dog/SonyBend/Incognito..ect) ,

Konami. Such greats ranging from old faves like Frogger and Track and Field to the modern greats such as MGS and Silent Hill, not to mension the great Suikoden series.

EA.Simply for the ammount of awesom games they have published... FIFA, Dungeon Keeper, The Sims, RockBand, Need For Speed, Crysis... the list goes on and on.

Naughty Dog. Crash Bandicoot, Jak and Daxter... 2 of the greatest platform genres EVER. The original Crash games imo are still the best platformers released, and the latest IP, Uncharted... is set for great things to come following the success of Drakes Fortune.

Naughty Dog
Kojima Production
NIS

Ensemble: Age of Empire and Mythology (that was them, right?)
Nintendo: Naturally
Clover: Okami

Sadly, two of these are no more.

1. rare(did u really not see this coming) everything they ever made
2.mistwalker; lost odyssey and blue dragon
3.bungie* halo series

* could also be replaced with capcom megaman x(best non rare game ever)

Sega- NiGHTS, Panzer Dragoon, Shenmue, Sega Rally, Virtua Fighter, Daytona, Shining games, Phantasy Star. 

Capcom- Resident Evil, Onimusha, Street Fighter, Ghosts' n Goblins, Mega Man, Power Stone.

Ubisoft- Ghost Recon, Rainbow Six, Far Cry, Prince of Persia, Rayman.

Dream Pod 9: Awesome rule system and Tribe 8 is a fantastic setting that is under appreciated.

Interplay: They really know how to push games forward and make them fun. Fallout was a masterpiece.

Rockstar: Current Masters of the Sandbox action game play. China Town Wars is a F'n amazing game along with VC and SA.(haven't played GTA4)

Nintendo: I know this is a 4th and I shouldn't list this. I find their games particularly uninspiring, but the level of pure polish for excellent game play is hard to match. So they get honorable mentions .

id: up until Quake 3

EPIC: just for the UT and Gears games.

Bungie: I love me some Halo

This is hard...

1) Nintendo: Love Mario Kart, Mario games, smash, zelda.

2) Namco: Tales games are awesome

3) SE: Some of there stuff sucks recently, but alot of their games are good and have been good, plus the remakes have been done very well. I buy alot of their games. World Ends with you, SO, FF, DQ, all good fun franchises. Hoping for more wii games from them tho.