Physics-based Particles via Geometry Shader:

This first effect is primarily used for waterfalls in Call of Juarez., and basically allows the game to create many particles without having to resort to using a lot of CPU power (so it's free to be used for other effects).

Below is a screenshot of the effect:

Soft-edged Grass and Leaves:

This is pretty self explanatory. All of the leaves and grass in the game have soft edges instead of the usual hard edge, which really cuts down on aliasing in the game.

Below is a picture of tree's and grass, and as you can see, there is no aliasing to be seen:

Dense Vegetation:

While this isn't exactly a DirectX 10 effect, it's still exclusive to the DirectX10 path in Call of Juarez. Again, this feature is self explanatory as it's basically just rendering more grass than the DirectX 9 version.

Below is a picture of a hill completely covered in grass: