National Trust for Historic Preservation Privately funded nonprofit organization to save America's diverse historic places. Benefits, get involved, historic places, historic travel, and resources.
Archnet Online community for architects, planners, and those in related fields, with emphasis on the Islamic world. They publish many free books on Islamic architecture in PDF format.
Center for Religious Architecture A forum for the study of the world’s religions through models of religious architecture. Features links to architecture books, opportunities to nominate religious architecture for modeling, and travel opportunities.