Many soaring web pages have a "links" section.  Below I've included only the sites with extensive collections of soaring links.

glider.com
Soaring Society of America - info. about every club and commercial operation in the U.S.
SoarWest
Thirty Thousand Feet Aviation Directory - Soaring

Links no longer active
Airman.com - SuperGuide to aviation web sites
dmoz Open Directory Project 
Dropbears.com
Flugplatz-Leibertingen - German soaring Links page with hundreds of links
gliding.start4all.com
Gulf Coast Soaring, Inc. 
Günther Eichhorn's Soaring Server
Landings.com
Whisperwings - Gliding Club in South Africa - Bruce Greeff
Worldwide Soaring - Details on places to fly gliders around the world - Christian Suttner