The thread asks for developers but most people seem to have just named publishers rather than individual devs. I'll do both just to be on the safe side.
Publishers:
1. SEGA - overall I think they are the most important and influential gaming company, created the 3D fighter, (arguably the) third person shooter and rail shooter as well as introducing the use of axonometric projection to video games, amongst many other important contributions. The six button lay out is still the definitive controller lay out to this day and the Saturn's dpad is still my favorite. Had a few down years but in the period in-between I became a PC exclusive gamer and I consider SEGA's output on PC unarguably some of the finest on the platform (Total War but now they produce CoH as well).
2. Capcom - Capcom at their peak is the only third party company where I think they would have been capable of supporting a console as a first party publisher. I hate them as they currently exist.
3. Nintendo - tons of important contributions to console and in particular, handheld gaming. Great content but in recent years I've been disappointed in them for a variety of reasons. Refusal to adapt to online gaming in a timely manner chief amongst those reasons.
4. SNK - lots of great fighting games and I love the NGPC/NGCD joystick, my favorite solution for digital control after Saturn's dpad.
5. Squaresoft - tons of classic RPGs and unlike some I still like them as Square Enix but most of the content I recognize as their best was produced as Squaresoft.
Developers:
1. SEGA AM2 - For Shenmue, Virtua Cop, Space Harrier, OutRun & Virtua Fighter mostly, to this day I think few games understand an open world as well as the first Shenmue. The objective shouldn't be larger spaces, it should be more content packed within a reasonable space. I don't enjoy traversing what amounts to pointless terrain and in most open world games with worlds that are too large I end up using the quick travel. If you have to include quick travel to get around your world, to me it seems you're admitting there's a flaw in the way you've designed your game.You're admitting all that terrain you designed for players to traverse, is rather boring. Give me more objectives, not the same amount of objectives stretched across a larger space. The travel is typically busy work, nothing more. I also consider Virtua Fighter the best 3D fighting franchise and the deepest and most intricate.
2. Smilebit - Jet Set Radio, Jet Set Radio Future, Panzer Dragoon Orta, The Typing of the Dead. Jet Set Radio is one of my favorite 3D platformers of all time (and yes, it's a platformer, not a skating game) and I view Panzer Dragoon Orta as the finest rail shooter of all time.
3. Sonic Team - Sonic, Sonic 2, Sonic 3&K, Chu Chu Rocket, PSO, etc. I know the last two Sonic games (on genesis) were developed at STI but the core members of Sonic Team were brought in to work on them, as such it's considered Sonic Team supported the development of the latter two. I consider the first three Sonic games the finest 2D platformers ever but I became extremely disappointed in the 3D games for being so linear. Sonic in 2D had some of the most expansive & open-ended level designs in a 2D platformer, especially within the 4th generation. The switch to 3D put Sonic on what essentially amounts to & in some cases literally, rails.
4. Clover Studios - Viewtiful Joe & Bayonetta but mostly Okami & Vanquish (I'm counting Platinum/Clover as one), I'm one of "those" people who thinks Okami is a better action adventure games than any of the Zelda titles (though I didn't play Skyward Sword and I still think Zelda is a fantastic franchise). Vanquish is just the best third person shooter ever made. It's amazing.
5. Relic - mostly due to vCoH, which is my favorite western-made game of all time. THQ was a monster this last generation, they were actually my favorite publisher for the 7th gen. Darksiders, Saints Row the Third, CoH, DoWII and I do consider the first Red Faction amongst the best FPS games ever but we're talking Relic right now, these guys are freaking fantastic. CoH2's off to a not-so-great start but people forget the condition CoH released in, and that it took ~2 years of patching to make it the best RTS of all time. I'm confident they can do the same with CoH2.
Tons of other devs I love who didn't make the list though: Team Andromeda, Overworks/AM7, EAD Tokyo (grp. 2, SMG2 is my 2nd favorite 3D platformer ever), EAD Kyoto (grp. 3), Treasure, Creative Assembly, Volition, Vigil, Valve, Capcom Production Studio 1 & 2, SuckerPunch (Sly 2 is my favorite 3D platformer ever but wasn't huge on Infamous), Naughty Dog, Bungie, Noise Factory, SNK, Squaresoft D1 etc. etc.