ArchInform: Database of worldwide architecture including built and unrealized projects.
Building Green: all about green architecture, worldwide.
Circular Worlds.com: Links to websites displaying panoramic imagery.
DesignInform Research Guide No. 1: Internet Sources of Biographical Information.
Digital Imaging Project: Art historical images of sculpture and architecture by Mary Ann Sullivan, Bluffton University.
Emporis: "Locate buildings in every country around the world." Great place for getting the facts concerning a building.
Europeana: "Explore Europe's Cultural Connections."
Fortified Places. Site about bastioned fortifications.
Galinsky: "People Enjoying Buildings Worldwide." Site started by students at the Harvard Graduate School of Design. Descriptive and practical information about buildings.
Great Buildings Collection: Good source for plans and 3D models of well-known buildings.
Historic Illustrations of Art and Architecture. Public domain images available for free downloads. Good for plans and architectural drawings.
Mimoa: Online Architecture Guide: "The world's modern architecture organised, mapped and waiting to be discovered by you."
Panoramic Earth: Panoramic views of cities and architecture around the world.
PlacesWire: "A curated feed of news and commentary on architecture, landscape and urbanism."
Ruavista: Signs of the City. Website about street life and architecture around the world.
Sacred Destinations: "Explore sacred sites, ancient wonders and religious places of the world."
Sites in 3D: Panoramic views of buildings in many different countries, including many Islamic sites.
Structurae: International Database and Gallery of Structures. Engineering focus.
Vitruvio. International architectural site covering all time periods. In Italian.