Where to get Occlusion Culling Tutorials?

Occlusion culling is a hot technique in computer graphics. Does anyone know where to get any source code with occlusion culling?

“take a look around” - limp bizkit

delphi3d.net had a demo, i think
nvidia has demos, i think
on this forum it was discussed, i think
on flipcode, it was discussed, i think
in the extension-registry, the occlusion-exts are listed, i think
google knows everything, i know

“take a look around”