Timothy J. Purcell, Ian Buck, William R. Mark, and Pat Hanrahan evaluate trends in programmability of the graphics pipeline and explain how ray tracing can be mapped to graphics hardware.
Eric Veach Ph.D. dissertation describes light transport problems in computer graphics and develops new Monte Carlo techniques that greatly extend the range of input models for which light transport simulations are practical.
Nick Rasmussen, Duc Quang Nguyen, Willi Geiger and Ronald Fedkiw presents an efficient method for simulating highly detailed large scale participating media such as nuclear explosions.
A PhD thesis in PDF format, introducing new volume graphics concepts. Includes background reviews of volume visualization and graphics. Also includes a specification of the vlib volume graphics API and describes volumetric ray-tracing.