These are links to websites that may interest you:
Preservation League of New York State
http://www.preservenys.org
Hudson River Valley Institute at Marist College
http://www.hudsonrivervalley.net
New York State Office of Parks, Recreation and Historic Preservation
http://nysparks.state.ny.us
National Trust for Historic Preservation
http://www.nationaltrust.org
Greenwich Village Society for Historic Preservation
http://www.gvshp.org
Central Park Conservancy
http://www.centralparknyc.org