Irises are good for a pond so are bullrushes and lilies and any other rhizomed plant,ie plants that spread via a thick underground(water) root.They are all heavy feeders and will keep the water clear once they are established,they do however,tend to take over and need keeping in check.They are planted in 'green' septic tanks where they can,if managed properly,clean the water to a usable condition.
Oxygenating plants,pond weed in general absorbs  sunlight and gives off oxygen,a must for all aquatic life,Try not to introduce wild weed from rivers etc as it could contain eggs or larvae of undesirables which if not in kept in check could wreck the balance of a pond.A tip,if it's not to late,is to dig the sides quite deep,this will keep wading feeders,herons and egrets etc out of the water.It won't stop them having a look though.