I was just thinking about this, and why Sunsoft don't get more love, specifically their fighting games. Waku Waku 7, Galaxy Fight and in particular Astra Super Stars (probably my all time favorite fighter, either it or KoF 97'). Team SANTACLAUS especially were underrated, and I don't see them mentioned much anymore (granted, not making games will cause that). Hardcore Gaming has a great retrospective on these: http://www.hardcoregaming101.net/sunsoftfighters/sunsoftfighters.htm
I'd also throw out Journey to Silius and Gimmick as very underrated Sunsoft games on the NES, especially for their soundtracks.
So with that in mind, who are some of the defunct, or just downtrodden developers/studios that you feel are worth remembering?
*Honorable mention for Atlus here, the only reason I didn't pick them is that they seem to be on the radar recently.