Two of my faves- water lillies and water iris. Both are submerged underwater.

I would avoid Canadian Pondweed as an oxygenator as it grows very fast and wants to take over. Nice basket plants are blue irises, marsh marigolds (I found the singles so better than the doubles) and Lithrum salicaria.These are all fine for a small pond.
Mimulus is really a bog lover but it seems to do OK in the lawn at the edge of the pond that is pretty dry most of the time, and it self seeds nicely too.

Water soldier, bog bean, acoris, water mint, lobelia cardinalis 'Victoria', are the ones I have in the pond all year round including ones previously mentioned.
How big and deep is your pond as some of the ones mentioned might be to vigorous for your space.

I've not noticed you on here for a while are you keeping well?

Don't forget the different grasses like catails. They are so pretty and the oxygenate the water for the fish, if you have fish.

Not my question, but really helpful answers! I have taken note as, apart from kingcups, my pond plants have vanished and I need to do something about it or my tadpoles will starve! Thanks!

Thanks everyone these are great suggestions!

As far as floaters, water hyacinth is worth considering as well as parrots feather. One thing though, they grow very quickly and need constant control as the weather warms up.

Parrot's feather is considered an invasive species here, so if you do buy it and then want to remove it make sure its composted and don't allow it to be dumped in water ways. though I am sure you are a fully responsible person Sewingkilla :o)

SBG is right. Into a plastic bag well sealed and into the garbage or into the compost bin. Parrots Feather is not supposed to survive below freezing temperatures but I have found out that it does. My ponds freeze over and it comes back every year. It can also grow very well in boggy soil conditions. Aside from that it is a very pretty plant that, if precautions are taken in its care, makes a beautiful addition to the water garden and surroundings.

it survives in my pond even when there is 2" of ice on the surface. it certainly does spread a lot but as said it composts really well.