I don't think you can beat
Kit and Ben Knotts . Take you a full day to get through that puppy.
The search term you want is probably "
marginal plants". First 3 I saw in Google looked pretty exhaustive, including the Knotts
marginal list site.
Then "
water lily" would be the other search that'll bring up a lot of good online catalogs.
Then "
floating pond plants" but Water Hyacinth is the only floater I know of that has a chance of flowering. Uncommon for it to flower in most cases.
Beyond that there's "
submerged pond plants" but they don't flower.
Keep in mind than when they say "shallow" or 6" or whatever for a marginal that this is the maximum amount of water above the crown. Deeper and the plants do less well and at some point die. However, virtually every marginal will do better with no water over the crown. Planting this way also keeps string algae from growing in and around the plants which is a huge mess. I would never plant a marginal any other way.
Shout out to a couple of my fav flowering marginals...
Canna,
Cannaceae, if you can get virus free stock. Constant bloomer, many colors, great foliage, big plants perfect scale for large ponds. Easy to reproduce. Here's some 8' tall Canna Wyoming planted in a bog.
Marsh Mallow,
Althaea officinalis. Almost a tree, and again, perfect scale for a large pond. Easy to reproduce from cuttings and very fast grower. Full of blooms all summer. Not on the Knotts list :sad:
I wouldn't over look terrestrial plants like one of my favs, Angel Trumpet,
Brugmansia. When planted next to a pond you can't really tell if it's in or out. Like most plants it's listed as toxic but my Koi ate the heck out of it. Flowers, leaves. They pulled in and broken off whole branches. So not that toxic. Flowers all summer, lots of huge flowers. Very fragrant at sunset, from a dozen feet away or more.
For large ponds I also like Gaint Reed,
Arundo donax. But it takes intestinal fortitude. Really has to be contained and kept after. But 15-20' tall in the first year, they're spectacular from a distance and awe inspiring up close if kept tidy. Great back drop for Canna.
Banana is also a great back drop. The flower is impressive but short lived.
Hope you tell us more about your plans.