How about horsetail, scouring rush, bunch of other names it goes by. I don't know if you're looking only for a bush (like the lilac)? But the horsetail is one of my favorites as a filler/accent in flower arrangements I bring in the house.

description: http://www.botanyworld.com/equisetum.html

picture: http://kaweahoaks.com/html/horsetail_rush.html

You could also try swamp milkweed (asclepias incarnata, do a google on that one...

Some nice shrubs for wet areas:
Buttonbush Cephalanthus occidentalis
Shrub dogwoods Cornus alba and sibirica
Summersweet Clethra alnifolia
Virginia Sweetspire Itea virginica
Deciduous Holly Ilex verticillata
Inkberry Holly Ilex glabra

It is a little weedy looking, but wild elderberry takes care of itself (once established), smells nice when it blooms, and likes ditches. I grow it on the edge of my yard because I am in to fragrance.

I have a low place where almost everything I planted died.I added compost first then planted joepye weed,lythrum,toad lily and queen of the prairie but I do have some late afternoon shade there-also have amsonia and an iris that likes damp and planted a native cane and that tall grass that looks like bamboo-those two have to go-they have done too good!Day lilies might do good there too.Posy Pet

you might try some cardinal flowers. I found some by the river and they are now happily growing by my well(have a leak) and they love wet soil. And they are so-oooo pretty. The hummers like them too.

Rough leaf dogwood grows along our stream. Here is some information.

Here is a link that might be useful: rough leaf dogwood