This is my diamond shader edited a bit (now mainly influcend by this shader: http://blenderartists.org/forum/showthread.php?252623-Making-some-jewelry). I tried to keep it clean and very simple. I hope you guys enjoy it!
BTW, the shader looks really nice with a HDRI. You can see how it looks with a HDRI and read how to use this shader here: Material Study: Diamond v2