1)Blizzard. I don't think there's a company that more appropriately demonstrates that quality > quantity. They literally started from almost nothing- one person literally did all the voice acting in WC2. It's not just that their games are good, they're great. You don't typically see a game that's both a good single and multiplayer game. It's even rarer to see one that gets supported by the company long after release. Seeing a game remain popular 10 years after the fact is almost unheard of on the scale that, say, SC, enjoys.
2)Nintendo. Without them chances are we'd either not have the video gaming industry, or that it'd be a far cry of what it is. Nintendo took a gamble and released their first console system in the US a few years after the Atari tanked and set a lot of standards that we take for granted today surrounding hardware quality and software quality. Not only are they innovative in the console world (they certainly didn't garner gamers in this current generation from astounding graphics, right?), but their games have most likely influenced something you've played. Mario, Link, Zelda, Samus, Luigi, Pokemon, Kirby... how many companies other than Nintendo can enjoy both successful console systems and well recognized software IP's? The only reason Nintendo doesn't beat out Blizzard is because of a strong tendency toward missed potential (Internets!? WAT?!) and a tendency toward shovel ware bloating.
3)Rare. Ok, fine, of late they've been a lack luster company. It'd seem as though ever since they got acquired by Microsoft their games have simply always had a "rushed" feel to them. Now, lets take a step back, and look at the broad spectrum. Golden Eye 007 easily defined the console shooter genre. Years down the line you look at games like Perfect Dark and the Time Splitters series and you realize you like it because at it's core its Golden Eye. But outside the shooter genres? Banjo Kazooie has an influence that goes far beyond the Nintendo 64- chances are an adventure game you've played drew something from it. If not Banjo Kazooie, than the much less reverent Conker's Bad Fur Day.