I've been away for a few days - Rob, they are good people at Octoraro, I've done some work with them.

I believe they provide the USFWS wetland indicator classifications for their plants in the catalog, it can be a good general guide to how wet each species likes it. In descending order of affinity for wetlands it goes:

OBL Obligate Wetland Species
FACW Facultative Wetland Species
FAC Facultative Species
FACU Facultative Upland Species
UPL Upland Species

Silky Dogwood is FACW, buttonbush is OBL.

If your area is a bit shady try winterberry (FACW).