Same as the RPG thread (home consoles only, owned IPs only).  Kinda surprising how strong they all are imo.

Xbox 360 (Microsoft Game Studios)

• PGR3: Project Gotham Racing 3 (Bizarre Creations) 2005
• Forza Motorsport 2 (Turn 10 Studio) 2007
• PGR4: Project Gotham Racing 4 (Bizarre Creations) 2007
• Forza Motorsport 3 (Turn 10 Studio) 2009
• Hydro Thunder Hurricane (Vector Unit) 2010
• Kinect JoyRide (BigPark) 2010
• Forza Motorsport 4 (Turn 10 Studio) 2011

PlayStation 3 (Sony Computer Entertainment)

• MotorStorm (Evolution Studio) 2006
• Gran Turismo 5 Prologue (Polyphony Digital) 2007
• WipEout HD (SCE Studio Liverpool) 2008
• MotorStorm: Pacific Rift (Evolution Studio) 2008
• ModNation Racers (United Front Games) 2010
• Gran Turismo 5: The Real Driving Simulator (Polyphony Digital) 2010
• MotorStorm: Apocalypse (Evolution Studio) 2011

Wii (Nintendo)

• Excite Truck (Monster Games) 2006
• Donkey Kong Barrel Blast (Paon) 2007
• Mario Kart Wii (Nintendo EAD) 2008
• Excitebots: Trick Racing (Monster Games) 2009
• Excitebike World Rally (Monster Games) 2009
• Art Style: lighttrax (Skip) 2010 

I would peg Sony's as the top, for breadth of types and for quality across that breadth, though Mario Kart Wii's 20 million combined with the pittance that the other games ran, probably puts them over all of Sony's sales combined so far (though as GT5 picks up, that will probably be offset)

While MS has the highest rated racing games, the PS3 just doesnt have a bad game on that list whille the other have some terrible games in that list.

Again voting for Microsoft.

PGR4 is still my favourite arcade racer of the gen and Forza 3 a really good racing simulator.

Sony only has GT5 in my opinion. Motorstorm series is okay but doesn't really stand out, again IMO.

Same with Nintendo and MK Wii.

The Wii has the best racing game.

The PS3 has the most diversity/quality ratio.

The 360 has just an overall great line-up.

I'd say a tie between PS3/360.

While I haven't played them, DK Barrel Blast and Kinect JoyRide are supposedly terrible, yeah.  The rest are all good to great though.

I picked Microsoft, mostly because I think they have the best balance really.  I love a few of the Nintendo titles (Mario Kart, Excite Truck, light trax) but they're all super arcadey.  Sony seems incredibly solid too really (and just as diverse as MS), but I don't think GT/MS have been quite as standout as Forza/PGR this gen.

Sony.

Modnation racers, GT5, and Motorstorm against MK Wii from Nintendo and FM3 from MS.

So, Sony.

Modnation racers and motorstorm make it sony for me, though I enjoyed forza a lot. (I have yet to play GT5)

While Mario Kart is easily my favourite of the list, due to diversity and good quantity of quality I'm voting Sony

Went with MS/Nintendo tie.

Nintendo dominates arcade style while MS dominates Sim style.