I think Nintendo has done so many great things for gaming, it is honestly difficult to count. I think I am just gonna say Super Mario. To me he is still essentially the face of video gaming.
Sony is a bit more mixed, they did a lot of small great things, but pointing to a really big one is harder. Maybe the dual shock controller?
Microsoft's greatest accomplishments are probably not even related to Xbox, but more what they did for gaming on PC. They certainly has done a great job building an operating system that is great for gaming. The biggest single leap was probably introducing MS-DOS.
So in short:
Nintendo: Super Mario
Sony: Dual Shock
Microsoft: MS-DOS








