Slides
http://www.slideshare.net/NVIDIA
http://developer.amd.com/gpu_assets/01gdc09ad3ddstalkerclearsky210309.ppt
http://www.guerrilla-games.com/presentations/Siggraph2011_MichalValient_OcclusionInKillzone3.pptx
http://www.crytek.com/download/izfrey_siggraph2011.ppt
http://www.humus.name/Articles/Persson_CreatingVastGameWorlds.pptx