I had the same dilemma and planted red twig dogwoods and forsythia, I also put in pacysandra and hostas for accent, not for erosion control. If you really want to control the erosion your best bet is to slow down the water by placing some rocks in the area. A less attractive option is ripwrap.

Illicium floridanum is a broadleaved evergreen hardy to 6b with red, pink, and white flowered varieties. Xanthorrhiza simplicissima is a low, rhizomatous shrub with fernlike foliage. Both do well in moist shade.

Mazus reptans could help as a grondcover. Also, some ferns will take wet feet. Itea, Virginia Sweetspire will tolerate shade and wet as well. Ilex glabra- Inkberry holly is another option. They tend to drop their lower branches, so need a facer plant.

You looking at trees and shrubs? Or perrenials? If trees and shrubs, check out the link below. It's a nursery here in MD that does pretty much only natives. And there is a nice reference as far as sun needs and water tolerance (for the water tolerance look at the FAC, OBL, FACW column). I like any of the shrub dogwoods, pretty much any viburnum, ITEA works, I even have Oakleaf Hydrangea in my wet area. The Hydrangea won't take much standing water though.

You could even go with an American Hornbeam tree if you have the room. An understory tree that has a really neat history in this area.

Here is a link that might be useful: Clear Ridge Nursery

Take a look at the sedges and rushes (Genus Carex). Many of these prefer wet feet and shade and there is quite a variety of colors and heights. Home Depot in Gaithersburg even has at least one variety pretty inexpensively. (They had two, but I bought a lot of one of them). Benhke's in Potomac has a great variety of sedges in their shade perenial section. I just bought a tall one from them that I hadn't seen anywhere else.

If it is really wet the rushes will do well and there are some pretty ones.

Willow trees grow quickly and like to be near water.

You might want to check out some of the Polygonum clan. They have very stubborn roots. Not the most decorative, though, and you will never get rid of them; in fact, some are considered invasive aliens, like Japanese knotweed.

Many bamboo also like to be near water, and some are advertised as being good at retaining soil. Some bamboos have ancillary uses as well, such as food (sprouts) or timber (poles). If you really have a powerful current to deal with bamboo might be an answer, especially the spreading kinds, for which much space is needed.

For decorative effect, don't forget primroses and lobelia syphilica; skunk cabbage looks like a big hosta and will take more dampness... Then, cattails and other marsh grasses... Sounds like fun!

Please try to plant natives or at least non-invasive exotics in riparian areas like that. The Clear Ridge link is excellent -- they're a wholesale nursery, but I've called in advance and driven up there and they were happy to sell me just a few things for my home landscape. Take a look at the publication below. It will give you a list of plants appropriate for this type of area -- many of them quite beautiful.

Here is a link that might be useful: Native Plants for Wildlife Habitat and Conservation Landscaping in Maryland