These are a few links you may find useful. The list is far from complete and in no particular order but should provide some good starting points.
NSA2009 - The 35th National Stereoscopic Association annual convention.
The National Stereoscopic Association - National 3D organization.
International Stereoscopic Union - An international stereo group.
Photographic Society of America - Stereo Division - Just what it says.
Atlanta Stereographic Association - Local Atlanta stereo club
Cascade Stereoscopic Club - Local Portland Oregon stereo club.
Stereo Club of Southern California - Local Los Angeles stereo club.
Amateur Photographic Exchange Club (APEC) - Stereo view exchange club
Digital Stereoview Exchange Club (DSEC) - Stereo view exchange club for "digital format"
Interesting 3D Sites:
20th Century 3-D - Information on old viewers and views.
3D by Dan Shelley - Good link site with lots of stereo related information.
Boris Starosta - 3D images some for sale.
Phantomphotos - Phantogram site
Stereoscopy.com - Good information source and gateway site.
Terry Wilson - 3D images for sale including Phantograms
View Master Homepage - "View Master" related information with some sales.
3D Supplies and Equipment:
3D Concepts - Suppliers of RBT cameras, mounts and projectors.
3D Stereo.Com - Suppliers of 3D related material.
Berezin Stereo Photography Products - Manufacturer and supplier of 3D related material.
Dr T's Stereoscopic 3D Site - 3D books and repair services.
Graphic Media Research - Manufacturer of the "PokeScope" viewer and software.
Reel 3-D Enterprises - One of, if not the oldest, suppliers of 3D related material.
Rocky Mountain Memories - Suppliers of "Spicer" mounts and other 3D material.
The Stereo Store - Supplier of 3D material, slide duplication and video services.