There are many great sites out there for modern architecture enthusiasts. An effort to be comprehensive is difficult, so I will add sites when I find them, or have the time.

Guides, Groups, Etc.

Los Angeles Conservancy Modern Committee - preservation group dedicated to the recognition, preservation, and revitalization of the historic architectural resources of greater Los Angeles.

Palm Springs Modern Committee - volunteer group dedicated to promoting and maintaining the heritage of modern architecture and design in the greater Palm Springs area.

galinsky - free access to exciting modern buildings and the
means to explore them: photographs, descriptions, books, and practical visitor information.

DOCOMOMO - international working party for documentation and conservation of buildings, sites, and neighbourhoods of the modern movement.

Richard and Dion Neutra VDL Research House 1 and 2 - two buildings my Neutra in Los Angeles open for tours. See site for dates.

Raymond Kappe Interviews - two interviews of the Los Angeles architect - one from 1976 and the other from 1997. Ron Kappe - Raymond Kappe's son is also an architect. This is the site for his firm in San Rafael, CA.

MAK Center for Art and Architecture - holds exhibits in the Schlinder Kings Road house. Check site for current events as well as info on tours of the house.

Yahoo!'s Alphabetical Directory of Architects

Magazines

Nest - my favorite shelter rag.

Dwell - devoted to modern home design.

Patio - inspired by Mid-century outdoor lounge culture: architecture, furnishings, food etc.

Echoes - originally called Deco Echoes when it was originally published in the heyday of Art Deco fanaticism - but now called Echoes since it is about anything modern.

Shopping

Modern Design Services - check out my custom furniture utilizing wood I-beam construction.

Yahoo!'s Mid-century Shopping Category