This is a screenshot of a basic path tracer (see Kajiya's SIG86 paper "The Rendering Equation") I have been writing. Notice the glass object, and how it refracts the light coming from the green object. The glass object is subject to Fresnel's equation, and its index of refraction is set to 1.6
Also note how noisy the picture is; this is due to the high variance in the lighting caused by the caustics (just out of view) the glass object traces. Therefore, I am currently in the midst of writing a photon tracer. The cool thing about photon maps is that you kill two birds with one stone, as it can reduce overall variance (better importance sampling), and it speeds up overall computations (by reducing the number of rays shot).
To speed up the computation of direct illumination, I have an idea which I would like to implement. But it's still a bit of a secret now. ;)