This will have to be a work in progress, but I'll try to include links to
http://yellowbarnstudio.com - Yellow Barn Gallery at Glen Echo Park, Maryland
http://alog.org - Art League of Germantown
These are -
http://historicmedley.org - Historic preservation and land conservation in the up-county, John Poole House General Store Museum & Gift Shop, Seneca Schoolhouse Museum, Poolesville Museum, Medley Press, Ag Reserve Map, lots going on.
http://www.montgomerycountrysidealliance.org - Keeps the effort to protect the Ag Reserve well organized.
http://www.mc-mncppc.org/historic - Montgomery County Historic Preservation Commission. Knowledgeable, helpful staff - impressive files on historic properties.
http://www.dnr.state.md.us/met - Maryland Environmental Trust. Along with the local land trusts (Sugarloaf, Carroll Manor), are invaluable resources for land protection.
http://www.countrysideartisans.com - Artist studios, fiber arts studios, smithy, joinery, winery and other creative folks.