Independent developers (Like, a handful of people. Perhaps even one guy.)
Sandbox: MineCraft : Reviewed 93 by review sites, 69 by users on Metacritic. Created by a single man, Mojang.
MMORPG: RuneScape: Formerly one of the most played MMORPGs in existence, it was only recently overtaken by Blizzard's World of Warcraft in terms of paying member population. Created by a single man, Andrew Gower, (He has since left the company he founded for RuneScape, and it has been acquired, the leadership has changed. IMHO the game was destroyed since then.)
Shooter: 東方 Project: One of the foremost bullet hell/top-down scrolling shooter games, and possibly the most difficult game series in existence. Created by Team Shanghai Alice, which consists of a single man (and alcoholic), ZUN.
Traditional RPG: Laxius Power/Force: Created by a single man, 'Indinera Falls', he created an epic series (7 games so far) following the adventures of a random adventurer named... Random. The Laxius Power series is free, but the Laxius Force series that continues the storyline has gone commercial. The series runs on the RPG Maker engine. The Laxius Force series is rated 89, 85 and 88 by users. Notable for having one of the largest party sizes in RPG history, as well as intricate backstories for every single one of the characters.
Traditional RPG: Master of the Wind: Created by three men. Volrath (storyline and gameplay), Artbane (gameplay and programming) and Enkur (art). Consists of 7 story arcs for hundreds of hours' worth of gameplay, centred on two wannabe superheroes... who eventually do end up becoming just that.
Small companies... but perhaps not for long...

Action RPG: Torchlight 1 & 2: Created by the programmers (and music composer) from the fired Blizzard North division, the new company Runic Games, while low in budget and lower in manpower, still succeeded in creating a game (TL2) many players believe is superior to Blizzard's 'blockbuster' Diablo III, which did well in critic reviews (88) and horribly at the hands of player reviews (37). In comparison, Torchlight 2 is reviewed 81 by critics, and 80 by players.
Simulator/FPS: MechWarrior Online: The first in the series in ten long years. Made by the Vancouver-based Piranha Games Interactive. This game.
Strategy: MechWarrior Tactics: Not too sure personally, but it looks to be a video game adaptation of the TableTop BattleTech. Made by the Vancouver (again?) based Roadhouse Interactive.
Adventure: Heavy Rain: One of the most innovative user interfaces of any PS3 game. The story also unfolds in response to your actions. Rated 87 by reviewers, 69 by users. Made by the France-based Quantic Dream.
Quantic Dream may or may not be releasing a game in the near future based on the storyline from Kara.
Artistic: Draw Something: The veritable iPhone sketch application. Made by a tiny company, OMGPOP. Since acquired by Zynga.
Shooter/Worms-like: Angry Birds: Rovio Entertainment. No longer tiny due to the massive success of the game.
Meanwhile, this is what the bigger studios have been doing:
Notable recent games created by major developers: Portal 2 (Valve), Dragon Age II (BioWare), Skyrim (Bethesda).
Recent notable PR fails for some reason or other by major developers: Mass Effect 3 (BioWare) [Ending], Final Fantasy XIV (Square Enix) [The whole freaking game], Skyrim (Bethesda) [Took an arrow in the knee], Dragon Age II (BioWare) [Incompatibility of savegames between DA2 and DAO between regions, making it effectively half region-locked, one of the most copy protection for ANY PS3 game out there], Diablo III (Blizzard) [Storyline, Real Money Auction House, Persistent Online DRM], StarCraft II (Blizzard) [Releasing one game in three installments].
Notable series continuations with very little change except graphical improvements between versions: KOEI (Dynasty Warriors Series), EA (Battlefield Series), Activision (Call of Duty), and the sports series NBA Live, Pro Evolution Soccer and whatnot.
Heck, the only major game development studio I still like is Valve... and more than half the reason is because they're helping small companies and independent developers publish their games through the Steam platform for very low cost, and thus giving them advertising and such exposure that would be hard to otherwise get.
So it seems the future of gaming is going to be in the good hands of independent developers and small game companies. At least, from my point of view. What do you think?