AirNav FAA Airport Database - U.S. Airports

Soaring Hotspot Project - Any interesting project to map locations with strong thermals using flight log files.

www.soaringdata.info - Lynn Alley, A great resource for creating airspace and waypoint files for any region of the US in a number of formats.  Also U.S. Sectional Chart files for use in SeeYou.

Worldwide Soaring Turnpoint Exchange - Soaring Waypoints & SUAs - Awesome collection of soaring waypoint and SUA data files - John Leibacher

Links no longer active.
Airspace - USA - Program for creating SUA (Special Use Airspace) data files for the US. - Carl Ekdahl
CanadaSpace - Program for creating SUA (Special Use Airspace) data files for the Canada. - Carl Ekdahl - Note: you have to scroll down a little to see the link to the Canadian airspace utility.
EuroSpace - Program for creating SUA (Special Use Airspace) data files for Europe. - Carl Ekdahl
FAA Office of Air Traffic Airspace Management - Data files available on CD for $36 for U.S. airports, SUA's etc.
Generating Your Local Airport Database - U.S. - Richard T. Schaefer
Just Soar - U.S. Airspace and Airport data for a fee