Title says it all

Bioware
So many Bioware games , so little time.
Neverwinter Nights , The Witcher , Star Wars : Knights of the Old Republic , Oblivion...
Bioware has given English RPGs a firm definition and standing in the markets , whilst it may not have displayed a firm standing in the storyline field but gameplay-wise , their games are pretty addictive.

NIS ( Nippon Ichi Software )
I have a fairly mixed opinion about this company actually.
They release some pretty decent goods like Disgaea and Ar Toncelio from time to time but also made rubbish like The Last Rebellion which can cause some pretty serious headaches with it's gameplay.
Their other releases aren't quite as prominent since their overshadowed by their major releases , but their actually pretty good to be honest.

Konami
Konami has released a large variety of games , but the most notable being that of the Metal Gear series , the Castlevania series and well , the Silent Hill series.
I'm pretty sure some of you guys would remember Contra as well.
Whilst their variety of game releases is large , it seems that Konami bears a greater potential in making more mature games for their fans.

Kojima Productions
Sure , Konami released MTGS , but Kojima was the one who made it XD
Still , I'm kinda worried about the future aspect of this company , they have pretty much worked solely on MTGS and have done little on anything else.
It's without a doubt the Solid series is coming to an end after all , even if they try to extend it , there's no escaping it.

Bandai Namco
Bandai releases a combination of RPG and action games , as well as Mecha games from time to time.
The Tales series , the .hack// series and the occasional Mecha games which we MAY enjoy..
Well , at least their improving on their mecha games over the years.
... Aw shuck , how can I forget about Xenosaga!
Though you gotta admit , these guys releases some pretty awful Anime games from time to time.

Capcom
My favourite company for some intense action games.
It is responsible for the release of fighter legends like Darkstalkers , Street Fighter and the vs Capcom series.
Not to mention being responsible for making some pretty decent survivals and some pretty decent action games such as Monster Hunter from time to time.
Sometimes a company doesn't have to make it out of their major field to make it big.

SEGA
Whilst this company doesn't make international releases as oftenly as before , you gotta admit that the Phantasy Star series , Valkyria Chronicles series as well as games such as Yakuza and End of Eternity ( Resonance of Fate ) has proved phenomenomal.
Not to mention that Project Diva has proved to be... getting more and more wide-spread by the day.

Atlus
Though Atlus , technically speaking , is no more , we would still love them for the Shin Megami Tensei series as well as their collobarative efforts with some companies to deliver one of the most epic JRPGs of it's time.
Not to mention it had released Catherine prior to it's merge.
One of my favourite Tactical games , Hoshigami , was also released by Atlus... though I kinda doubt you guys know about it T_T

Square Enix
Whilst I do hate them for messing up the Final Fantasy series , you can't deny that they had made some of the best JRPGs that outmatches other similar companies.
They had released games like Dragon Quest , Valkyrie Profile , Star Ocean , collaberted with Atlus for the Shin Megami games , Parasite Eve , The Last Remnant... you get the idea.

Arc System Works
Whilst most of you guys would remember this company for BlazBlue , I'd remember it for Guilty Gear.
Why , I'd hate them forever for making someone like Bridget.
... Come to think of it , Noel kinda reminds me of Bridget.
Don... Don't tell me...
Nah , let's not think too much about it.

Ehh , I'm pretty sure I'm missing something here but... no matter , there's too many companies to remember anyway XD