Here's a nice grasshopper-imitation that was taught to me by my friend, Kaj Kirkeby. I'm not entirely sure if Kaj invented it - it might be a Bill Logan pattern?
Never the less, it works really well. Tied mainly with foam (and some medallion sheeting and rubberlegs) it floats quite well. If you've ever seen a grasshopper struggling in the water, you'll have noted that they don't float too well, and certainly not high. So in order to compensate for that and have a fly that floats in the surface rather than on it, I tie mine on a nymphhook with some weight, making the fly sit nice and low in the film.