Oh...too many to choose from. Maybe my favorite part of the pond....at least before coming to Phoenix. Our climate is a bit too harsh for many...but not all.
Canna does slowly multiply and by far my favorite. Almost impossible to get virus free at retail so best source are fellow local ponders and neighbors. Normally these are pre-virus. You get the big leaf tropical look, great flowers imo and can get different heights. Here 8' tall next to 2-3' tall.
Society Garlic, Calla Lilly (all kinds), Freesia, Impatiens (some big exotic looking), Pickerel, lots of grasses, Horsetail, lots of Irises, many others. I'd try any plant, most non-traditional pond plants work as long as kept up a couple inches above the water level. I keep water level below gravel surface so I never have string algae issues.
The woody trunk plant in this pic is a Marsh Mallow that I called Rose of Sharon because the ponder who gave it to me called it that. Great to have a tree growing in a bog imo. Needs good pruning to keep the shape you want and provide some shade if needed. Blooms all summer.
My smallest bog ever was a bird bath stayed water filled from sprinklers. Sedum, Irish and Scottish mosses. Everyone in the world will tell you Sedum will rot, and it can. But kept in soil and above the water level it can work. I think pretty much every plant will. Can't remember one that didn't and I tried many.
There are also many that will spread far and fast if conditions are right...but easy to cut back if you can give an hour every couple weeks in summer. Easy to pull stuff out of a bog. And really, IMO, you do have to pull almost everything at least once every 2 years or so to divide and thin if you really want the best show. Yeah, it can be left a lone for years and years but generally doesn't do as well imo. So spreading in that case isn't a huge problem.