Kojima Productions for me. The Metal Gear Solid series has been an absolutely HUGE part of my gaming life, and Zone of the Enders: The 2nd Runner is one of the craziest and coolest games I've ever played. Their games rarely disappoint me, and I feel that their games are more interesting and developed at a higher level than almost any other studio's. I eagerly await whatever it is Kojima and co. do next!
--Honorable Mentions:
No studio has a "spotless" track record for me (not even my favorite), but Squaresoft (NOT Square Enix) ranks very high for me. I adore Final Fantasy X, Vagrant Story, Chrono Cross, and Kingdom Hearts (the original).
Sony gets a lot of flack, and they deserve a lot of it for their often-crap marketing and ridiculous management, but their development studios are world-class. Naughty Dog has always been a very generic group in my eyes, until they rocked my face off last year with Uncharted 2. Sony Santa Monica's God of War series is, well, the best hack-and-slash action/adventure series ever made. Team Ico is, well, okay, "spotless" so far. :P Sucker Punch's InFamous doesn't do anything for me, but Sly Cooper is one of the best platforming series out there, especially Sly 2: Band of Thieves. One of the best platformers of all time! So yeah, Sony may not be as consistent as a Blizzard, but at their best their games are damn near peerless and as a company their stable offers a lot of variety.
Last up, Nintendo. Zelda, Mario, Kirby, Smash Bros., Pikmin, Metroid, etc. Not every game in those series' is good, but the ones that are tend to be about as close to perfect as games get.