I didn't know anything about water gardening other than I wanted lily pads for the frogs. Here are some of the plants we bought from the local pond store or ebay.

Many aquatic plants have the potential to be invasive. Luckily my pond is completely isolated from other wetlands.
One thing I have learned about goldfish and plants is that if you don't feed the goldfish, they will rip apart the roots of your aquatic plants. I've now enclosed my plants in a floating mesh which looks terrible but works well.

Water lily

Water Lettuce

Duckweed

Water Hyacinth

Creeping Jenny

Frogbit