Trail Runner Magazine Online
Running, health, travel, and training, race results and race event calendars.
http://www.trailrunnermag.com/

American Discovery Trail
Learn about the first running trail that crosses the entire nation.
http://www.discoverytrail.org/

Run Hayward Hills Trails
Trails of Hayward, California. Great for running and riding ATB.
http://members.tripod.com/sr_science/run_hayward_hills/

Northern Arizona Trail Runner's Association
Promotes trail running in Northern Arizona, in the United States. Includes a listing of upcoming races, related links, history of the organization, pictures, membership details, race summaries, and message board.
http://www.natra.org/

Team Gloucester
Trail running club in Gloucester, Massachusetts. Cape Ann trail information and maps as well as an extensive trail race calendar for New York and New England.
http://www.teamgloucester.com

Redwood Trails
Information on a series of trail runs in the Bay Area of California. Race distances range from 5k to the marathon.
http://www.redwoodtrails.com

Perry Scanlon's Home Page
Contains photos and links to trail and workout information near Palm Springs, California, as well as specific information for the Skyline Trail.
http://www.geocities.com/cactus2clouds/

Irish Mountain Running Association
Irish mountain running. Trails, races and links on the Island.
http://www.imra.ie/

Shenipsit Striders
Trail running club in Somers, Connecticut, sponsoring the Soapstone Mountain races as well as weekly training runs. Includes race information and results, photos, and links.
http://www.shenipsitstriders.org/

Gil's Athletic Club
Trail running club based in Topsfield, Massachusetts, sponsoring several trail races (primarily ultras). In addition to race information, includes weekly runs, guide to area trails, and photos.
http://www.gaconline.net/

Albany Running Exchange
Trail running club based in Albany, New York. Includes summer trail run series, results, calendar, photos, and member news.
http://www.albanyrunningexchange.org

Western Mass Athletic Club
Trail running club in western Massachusetts. In addition to club news, includes information for several trail and snowshoe races as well as the Grand Tree Trail Race Series.
http://www.runwmac.com/

eHow to Choose Trails for Trail Running
Tips and information about trail running. Requires free membership.
http://www.ehow.com/how_14503_choose-trails-trail.html

USTrailrunner
Includes gear reviews, race calendar, online store, and discussion board.
http://trail.ustrailrunner.com/

Peak Trail Runner
A guide to trail running in the UK Peak District national park.
http://peaktrailrunner.freehostia.com/