San Francisco Landmarks - A "photographic archive of San Francisco's historic landmarks as they appeared at the beginning of the third millenium." Presented by NoeHill.co - http://noehill.com/sf/landmarks/default.aspx
Historic Landmarks - List of local landmarks compiled from national, state and city sources. - http://www.sfgenealogy.com/sf/history/hgreg.htm
California Landmarks - San Francisco County - List of the California State Historical Landmarks in the City, along with photos of some of the plaques. - http://www.sonic.net/~laird/landmarks/counties/San_Francisco.html