Crytek has posted an interesting technical presentation showing their work on real-time indirect illumination. Very cool stuff.
Cascaded Light Propagation Volumes for Real Time Indirect Illumination
Authors: Kaplanyan, A. & Dachsbacher, C.
This I3D 2010 paper is a result of collaborative research with Carsten Dachsbacher. The LPV technique was extended to support secondary occlusion and multiple bounces. The propagation scheme is improved and compared to similar Discrete Ordinate Methods. Also this paper describes many additional application and implementation details.