If you want sometime showy, as in colourful I would plant an ixora coccinea, or hybiscus species. It would also be my suggestion to definately get some ficus primula over the fake rocks, this will definatly make more realistic. If colour was not your thing than i would go a colocasia (elephants ear plant) which once estamblished should look cool with a bit of the water drops running over the top and cascading down the plant as well.
All these suggestions or based on the perfect site that i have pictured in my head, you may have to keep other enviromental factors in mind. Good luck, Post a pic if ya can.