A full article that presents every aspect of implementing billboarded grass fields in games. It uses a vertex shaders for animating the grass in the wind.

Here’s the full article for free (also the source for the image). Or you could buy the great book “GPU Gems 1″ which also contains the article.
http://http.developer.nvidia.com/GPUGems/gpugems_ch07.html

An implementation of the grass rendering by Nvidia:
http://developer.nvidia.com/object/nature_scene.html