Over the long haul:
Nintendo - Of course, for all of the iconic characters and games they have contributed to video games as a whole.
Atlus - Just seeing their name on the cover of a game has usually assured me that I will enjoy it.
More Recently:
Bioware - They have created some pretty immersive open world rpgs.
If you asked me about 15 years ago:
Koei - I used to love their Historical Simulation Series before they reverted into an almost Dynasty Warriors only developer. I was pleasantly surprised when they released Bladestorm though.
Squaresoft (now Square Enix) - I greatly enjoyed the first several Final Fantasy games, but they also used to develop other great RPG's like Secret of Mana. Now, it seems like they are just interested in milking their cash cow (FF).
