So I started writing the shader for the grass on my terrain generator. So far it uses a shell system, but I'm hoping to incorporate fins to make it look better from up close. It's a 10 pass shader ( CRAZY INEFFICIENT) that renders the base texture blended surface, and 9 separate shells extruded outwards from the mesh. So far it looks good, but I'm still working on making it draw grass in different densities depending on the altitude of the terrain, so that cliffs won't have grass on them.

The good thing about using a shader for drawing blades of grass, is that it doesn't drastically increase the polygon count, and (if written correctly) will look good from any angle, whereas if you were using flat billboard meshes, the blades of grass might be in a perfect line and look flat from the sides.