Platinum Games - Possibly my favorite developer right now. Love the ridiculousness of their games.
Nintendo - I know they have multiple developers there, but most of them are great enough that they may as well be under the same lable. Mario Galaxy 2 is possibly my favorite platformer of all time.
Criterion Games - Developer of the Burnout series. Sadly because of EA being EA, they're now mostly working on new Need for Speed games. And while their NFS games are still really good and are actually a lot like their Burnout games (Most Wanted especially), it feels like they're also limited by the brand. Just compare Burnout Paradise and NFS: Most Wanted, you can see that they could go a lot more crazy with Paradise. Regardless, they're still a great developer and a bright spot in EA's list of developers, at least until EA fucks them over.
Double Fine Productions - Though the gameplay in their games can be lacking, they're some of the best when it comes to style, character and humor. I do kinda wish they'd make more big retail games, but their smaller games are still great. The only game by them that I found disappointing was The Cave, which was just tedious to get through and pretty hit or miss when it came to the humor.
Telltale Games - Yup, Walking Dead is great, but I honestly enjoyed some of the other episodic games before it more. Specifically Sam & Max: The Devil's Playhouse. Their Sam & Max games are pretty good in general, besides the first couple of episodes of the first season. Their Monkey Island, Strong Bad, Puzzle Agent and Wallace & Gromit games are great as well. The Back to the Future and Jurassic Park games were disappointing though, especially the latter.
Capcom - When they aren't being shitty. Put them here mostly because of Mega Man and Ace Attorney.
Naughty Dog - I love Crash Bandicoot, the first Jak & Daxter and the Uncharted games. The Last of Us also looks incredible. I consider Jak 2 to be one of the worst sequels ever though, and I haven't played Jak 3 nor Jak X.
Valve - They made Half-Life 2, Portal 1 & 2, Team Fortress 2 and Left 4 Dead 1 & 2. Enough said.
Bizarre Creations - RIP. I consider Blur to be the best kart racer out there, along with Sonic & All-Stars Racing Transformed. Makes sense that Transformed that directed by the lead designer of Blur
. Also PGR and Geometry Wars.