Insomnic Games- The dudes who made the Ratchet & Clank series.
Frictional Games- The dudes who made the Penumbra series and Amnesia: The Dark Descent.
Other companies like Bethesda,Sucker Punch,Naughty Dog are pretty popular now and that's why I don't think they're as under-recognized as the ones I've listed.Come on,practically every game Bethesda makes is Game Of The Year now(obviously,the ones directed by Todd Howard)!I used to think Sucker Punch were under-rated when they only used to make the Sly games,but the inFamous series has kind of exploded so,yeah.Not much to say about Naughty Dog either,yes,they used to be under-rated like Sucker Punch,making only Jak & Daxter games,but they've moved on to Uncharted,the no.1 PS3 exclusive.Too bad Insomniac Games,the member of the PS2 Tag Team(along with Sucker Punch and Naughty Dog,for the Ratchet+Sly+Jak thing) still haven't made much progress,because they can't leave Ratchet & Clank alone and move on.