I usually use several modelled grass objects inside a single surface replicator - that creates realistic diversity. I have also used modifiers on those objects (like punching or bending modifiers) to create wind effects. (if you do not randomize the orientation of your replicated objects, or randomize it very slightly without radical rotations, they will all bend in the same direction - like realistically windswept grass). If you want to take a look at my gallery, I have used this method in "You've Got Mail", "Personal Space", "It ain't easy being green." and "Odin of OZ" images.