Marsh marigolds like wet places, but if it gets too dry later they may not like that

Something I have always wanted to grow but can't because it's to dry here, primroses. Ligularia also likes moist soils. I also have anise-hyssop and it likes moist soils. Have you considered a shrub willow, Dwarf Arctic Willow 'S. purpurea 'Nana'? It only grows 3-4' and has deep blue foliage. Marg

In a sunny location, how about one of the hardier hydrangeas, such as Annabelle - they love water.

If you have a shady spot, I would recommend Ligularia. It has the advantage of being a herbaceous perennial so it dies to the ground in the fall but comes back in the spring, and with time will get to be quite large - about 5 feet in height.

Irises are not a shrub, but they would be quite happy in a sunny, soggy location.

I thought of irises too, a Siberian or a flag species. I used to grow Iris versicolor and it was really nice. Some of the Sibs are very tall and would fill space well.