Marcos, the creator of the Arnold renderer in use at Sony Pictures Imageworks was recently interviewed. Fun read. In an email conversation with him, he pointed out some recent papers he was directly and indirectly involved with. They too are worth reading if you are into raytracing.
Physically-Based Shading and Lighting at SPI
Siggraph 2010: Course on Global Illumination
And for added fun, here are some wayback renders done in the early versions of Arnold for 3dsmax. Some of which I did;)