Gunnera, Chilean rhubarb, is gorgeous. We have a big lot of it growing on a small island in the middle of the stream that runs through a local park but it has invaded coastal cliffs, stream margins, wetlands and slip faces with the large leaves shading out natives. You need to check with your local council to determine its status in your area.
As alternatives, the National Pest Plant Accord suggests you look at Swamp Astelia, Astelia grandis, or Chinese rhubarb, Rheum palmatum. :thup: