Fabulous prismatic rainbows of fabulousness. Not just RGB, THE WHOLE RAINBOW.
Sorry for the poor render, will render it overnight to see if the mess that is the interior converges properly.
Update: Organized the nodes, fixed some stuff.
Update 2: Changed the object to a triangular prism because duh.
Update 3: I don't like the lack of vibrance to the dispersion, upping the delta amount and seeing if that helps. New image.
Of course if you use LuxRender instead of Cycles you can get this effect natively, without heavy node setups. Still, this is an interesting case study demonstrating what the node system can accomplish if you push it to the limit, you have effectively implemented a new feature (dispersion) for the renderer using just the node editor.
Edit: oops, meant to post this as a general comment and not as a reply to the above comment.
very cool I didn't know you can do that in blender.