Nintendo:

1. Harvest Moon
2. Sonic (Duh)
3, Just Dance (I dont want it, but it should be really :P)


Sony:
1. Final Fantasy
2. Metal Gear Solid
3. Assassins Creed

I disagree with everyone who says Nintendo should own Sonic. Heck no. What good would that do? Nothing. I don't see how a Mario-like Sonic would work. Lost World was close enough.

Who said 'Mario like'? Because that would be fairly poor a call. Sonic is as different from Mario as Kirby is. - Granted that does suggest that they'd be willing to keep Sonic as a 2D game like Kirby is, not to say that would be a bad thing. Still I think SEGA have layed enough ground-work that Nintendo could take the highlights (like combining racing and platformer ideas, and adding mutliple paths) and make a very well done game.

That said if they did decide to take more inspiration from Mario than SEGA have in recent years (give him a Princess to save, give him more power-ups, give him cylindrical levels - only one of which really enhanced things, namely Colours) I'd LOVE a 3D Land esque Sonic, it would basically play like a 2D Sonic with a 3rd dimension.

Actually I'll take Sonic 3D Land and Kirby 3D Land if its not too much hassle. 

Yeah, it is, and that's what you get when a Sonic fan makes a reply too fast.. Well, you see, I had this discussion once with a fellow Sonic fan when Lost World was released about Sonic having too much of a Nintendo influence in that game. It's hard to put into words why because it was quite an extensive discussion but we both ended up agreeing on it and since then I don't really want Nintendo to take over Sonic. It might honestly just be me though, because I'm a Sonic fan. You know how we are..

Crazy, passionate, wierd, and in constant distress over the poor fellow. - I really liked the two Adventure games on the Gamecube and got a good bit into the series. Heroes and Shadow (love the character, definitely don't love the game) nearly pushed me away, but then Secret Rings and Colours won back my interest. That series is absurdly hit and miss.

That's an interesting question.

Microsoft:
Ninja Gaiden
Call of Duty
Mass Effect

Sony:
Metal Gear
Final Fantasy
Devil May Cry

Nintendo:
Harvest Moon
Dragon Quest
Monster Hunter

Sony:

1. Persona
2. Final Fantasy
3. Metal Gear Solid

Nintendo:

1. Mega Man
2. ?
3. ?

Can't think of any more for Nintendo.