Reducing Polygons in a high detailed models

3D modellers - I have a project that has highly detailed models. does anyone know a auto-simplifying way to reduce polygons or a simpler way to do this in Cinema4D or by any other means?

I feel like every modelling related question I chime in with something about Sculptris and I'm going to do it again :)

Sculptris has a 'reduce brush' and 'reduce selected' tools you can use to reduce the polygon count. You should be able to import your model into sculptris and use those.

http://www.sculptris.com/download.html