The WebGL standard is developing to allow 3D graphics on the web. Unfortunately, it is currently only available in developmental branches of major browsers. In the mean time, the HTML5 Canvas element provides support for 2D graphics... unless you have a backend library to render 3D scenes. Lookie what I did. You'll need a good browser... anything other than IE will do. Drag the display pane to rotate; use the mouse wheel to zoom in/out.
In other news, I've discovered that I remember close to nothing about 3D geometry.