I'll list my favorites and standout games and/or reasons why I like each.
Quantic Dream
Indigo Prophecy
Heavy Rain
Just a unique developing company
Electronic Arts
Too many games to list honestly. But mainly the sports games they develop. My all-time favorite sports game NCAA Football 2006 is a huge reason. Overlooking the most recent installments of Madden and NCAA, otherwise all their sports titles are top notch in terms of content and gameplay.
Enix(RIP)
Valkyrie Profile
Star Ocean
Dragon Warrior/Quest
Atlus
Persona
Growlanser
Thousand Arms
I more just have an appreciation for Atlus, because they bring over a lot of games to english audiences that otherwise never would have made it.
Sony Computer Entertainment
Again too many to name here, just random games here and there like Legend of the Dragoon. They are really more of a publisher, but I do have an appreciation for their overall body of work.
Ubisoft
Rainbow Six 3
Rainbow Six 3: Black Arrow
Splinter Cell
Ghost Recon
Various other Tom Clancy Games
Beyond Good & Evil
Other random games here and there, they have a lot to name
SEGA
Sonic the Hedgehog
Shenmue
Jet Grind Radio
Phantasy Star Online
etc
Capcom
Street Fighter
Resident Evil
Devil May Cry
Marvel vs Capcom
Megaman (Megaman Legends!)
etc
Konami
Zone of the Enders
Silent Hill
Dance Dance Revolution
Contra
Pro Evolution Soccer
Midway
NBA Jam
Mortal Kombat
NFL Blitz
Ms. Pacman(the best arcade game ever!)
Basically just an amazing arcade type game developer, just plain fun.