Hodgman: fantastic! What wonderful examples - I'm really keen on that Nvidia one.
ddn3: Windows only! I was unable to open the exe, but working with Unity sounds fantastic.
Seeing Arauna's list though: Do I need any special features to have the light curve in the glass? I have no experience with that, just a lot of curiosity.
Yep Arauna is a full path tracer which will reproduce the proper caustics of glass. That is the fun thing about raytracers, no tricks required to reproduce these complex light - object interactions and reflections. There was an older version of Arauna, see if its still out there.