WebGL, or some engine using it (didn´t Unity have some WebGL export option or something?). WebGL is quite perfect for something like that, the problem is just that it is only fully supported by Chrome and Firefox, last time I checked it was enabable in Safari and supposed to be there in Opera soon, Internet Explorer however won´t have it too soon due to security concerns
Then there also is some drawing functionality with HTML5 which should have wider support already, but it probably isn´t sufficent for more complex model rendering than a few cubes. So what you are left with for now is most probably flash...