Vallisneria, Corkscrew (Vallisneria americana var. biwaensis) (10 plants per order)
http://www.aquariumplants.com/product_p/va069.htm
is what I bought and planted about a month ago. My pond is clear so the sunlight can reach the plants. I planted 100 plants around the pond but I have three plants near my deck so I can watch them every day. They have probably doubled in their area size in this time period, which means instead of two grass blades they may have four. I'll have to wait until next year to tell if they are really going to take hold.