Flash, Silver light and now OpenGL on the web, http://www.khronos.org/webgl/ but this one is open standards and based on OpenGL engine. More information can be found the link above.. cannot wait for it to come to light and see what is the major player in the market place.
You might like to check out this scene graph framework for WebGL:
http://www.scenejs.com –
It’s a very active project in development. Two of the principle advantages to layering a scene graph on top of WebGL is abstraction and transparent optimisation. A graph API helps automatically organise many of optimisation strategies like memoisation and lazy-computation, while also providing a simplified API for describing 3D content.
Cheers