Clethra alnifolia (Sweet Pepperbush, Summersweet)
This native North American spring flowering shrub, with fragrant, white racemes and yellow fall foliage is just the ticket for poorly draining soils, as its natural habitat is wetlands.
Clethra alnifolia, or Sweet Pepperbush, is slow to get established, but once it settles in, it's easy to grow and attracts butterflies, hummingbirds, and bees. Birds enjoy the seed heads in fall. Sweet Pepperbush grows from five to eight feet tall in full sun to part shade and in moist to wet soils. Prune in fall or early spring, as it blooms on new growth. Zones 4-9. (Illustration by Janus (Jan) Kops [Public domain or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons)