Playcanvas, an up and coming HTML5 Game engine, is making some waves on the scene by pulling off 3D development. It currently utilizes WebGL so IE is not supported, but you can bypass this with Google Chrome Frame if needed.
I took about five minutes to play with the engine, and felt it was definitely a good beginning, and I can’t wait to see what these guys can do. Check out the D.E.M.O. they have been working on for a preview of what the engine can do.