Answer: To keep a healthy balance in your pond you will need a good number of oxygenator plants such as anacharis, as well as plants to shade about two thirds of the surface. Hardy water lilies will do this nicely.
You may also add large architectural plant such as a water lotus and more intermediate plants such as dwarf cattail and parrots feather and so on. All of these are hardy. Water hyacinths make a lovely addition, too, although they are not hardy. Some of the marginal plants such as taro and papyrus are lovely but also are not hardy so you will need to decide if you want to try to keep them indoors or replace them from year to year or skip them. You will also have to decide if you want your pond to be more of a pool of water or more of a large container for water plants -- it's easy to add too many plants.
In my experience all of the above plants are very easy, simply pot them, pop in a lily tab or two according to the label instructions, remove any faded foliage and faded blooms as they occur, and enjoy. They will also help keep your pond algae free and the water clear. Remember though that water lilies prefer still water so need to be placed away from any fountain you may have.
Some gardeners find that a combination of rocks, dwarf conifers and creeping type plants such as thyme make a nice transition to their pond, others prefer a more floral effect and use all sorts of sun loving perennials (daylilies, sedum, purple coneflower, small grasses, achillea, etc. would all do well). Still others go for a tropical look and use bold plants such as cannas, ornamental grasses and ornamental sweet potato vines. It's really up to you because your pond can be surrounded to integrate with the rest of your landscape in almost any style. Have fun!
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