Haven't seen any of these kinds of topic around in my nearly-two-months on this site, so I thought I'd open it up for discussion.
Hopefully it won't descend into a console vs. console flaming war, but I'm interested to hear who everyone thinks are the best (or at least, your favourite :P) development studios of all time. It seems to getting harder and harder to track a single studio these days, since more often than not they dissolve and reform (i.e. Incognito Entertainment -> Lightbox Interactive, Bizzare Creations -> Playground Games), but I still thought this was worth a shot.
So, my list (along with the games that made me fall in love with them, and why I love them):
Bullfrog Productions (Theme Hospital, Syndicate Wars, Populous: The Beginning)
When I was younger, aside from playing just platformers, I had a real drive to play RTS/Sim games. I don't even know why. To this day, I still find their games incredibly playable, and still the leading examples of how to do the genre correctly. The way they mixed humour in their games was just incredible, too (Theme Hospital, Dungeon Keeper). I really miss Bullfrog.
Nintendo EAD (Pikmin, Super Mario Galaxy 2, Mario Kart: Double Dash)
It's hard to define just one Nintendo studio since there are so many working next to each other, and it's not always easy to see who makes what. That said, I just kind of blanket-statemented all of Nintendo's studios since I think they've all done amazing work. I can go from something light-hearted like Mario Kart to something deeper like Pikmin and love every minute of it.
Insomniac Games (Spyro: Year of the Dragon, Ratchet & Clank: A Crack in Time, Resistance 2)
At a time when all my friends were fawning over Crash Bandicoot being the best thing ever (we were about 8, to be fair), I was playing Spyro the Dragon. I guess my avatar shows that I'm a pretty big fan. The way Insomniac carried that child-like, collectathon gameplay over to the Ratchet series was just great - it felt like Spyro, but improved in almost every way. And they've stuck with it and given me countless new iterations to play. I think Insomniac are an incredibly talented studio and I look forward to Overstrike.
Naughty Dog (Crash Team Racing, Jak II: Renegade, Uncharted 2: Among Thieves)My love for Insomniac, though, isn't to say that I haven't enjoyed Naughty Dog's work - it's hard to like one without liking the other! It's been weird watching Sony's injection of money into the studio and having their games slowly grow in scope. I really enjoyed the Jak series on PS2 (the second game being my favourite), but the studio really blossomed this generation with the Uncharted games.
Japan Studio (Ape Escape, Rogue Galaxy, Demon's Souls)
Sony's Japan Studio is kind of a hard one to pin down, because they work on a multitude of things (much like Santa Monica) but don't have a particular 'base product'. Their Ape Escape series has been what I've liked most so far (I love platformers), but they've worked with Level 5 on numerous JRPG's (Rogue Galaxy being the best, in my opinion) and assisted on Demon's Souls, which is a fantastic product.
So, that's my admittedly Sony-biased view at the best videogame developers ever, who are everybody else's favourite studios?