Another...rather tedius way...is to make lots of little polygon planes; 1x1 grid is fine...maybe scale them up so that they're 2-3 times as high (or more) than they are wide. Create a decent grass blade texture in photoshop (or even a flat green color will do), with an alpha channel around the blade of grass (or green).

Assign the grass texture to the plane, and duplicate it like mad...:mg: