If you have a shallow pond I would be careful putting anything in them. If not then a some lilypads, bulrushes, iris should be fine. Make sure if you use the fragrant water lily instead of Spatterdock. That plant looks like a lily but the leaf comes out of the water. Its a little more aggressive. See first pic below.
Use these
Bulrush,
Fragrant Water Lily
Blue Flag Iris