Check out the Maryland Native Plant Society (www.mdflora.org)  The website has a lot of good information about native species to plant -- and ones not to plant because they are invasive -- plus a list of local growers and propagators of native plants.  In addition, the society's monthly meetings cover a range of interesting topics, and the field trips help acquaint you with native species, both common and rare.

Jane Hill
Bethesda, MD