Glass Steel & Stone
http://www.glasssteelandstone.com/
While some web sites focus on skyscrapers, or monuments, or castles; Glass Steel & Stone encompasses all great structures that are aesthetically pleasing.

Great Buildings Online
http://www.greatbuildings.com/
Great Buildings Online documents hundreds of buildings and leading architects with 3D models, photographic images and architectural drawings, plus commentaries, bibliographies, and web links, for famous designers and structures of all kinds.

Digital Archive of Architecture
http://www.bc.edu/bc_org/avp/cas/fnart/arch/
This site maintains a collection of scanned images from throughout the history of architecture.

Architects USA
http://www.architectsusa.com/
Architects USA is an Internet directory of over 30,000 architecture firms in the United States of America. The listings are from the Yellow Page's and from architects who have sent in their information.