State Focused Forums
Michigan Equine Lovers - This is an incredibly active board. They average well over 250 messages per day!
Michigan Trail Riders - This is the organization that is responsible for the Michigan Shore-to-Shore trail, which goes from Oscoda (Lake Huron) on the east to Empire on the west (Lake Michigan). The link takes you to their home page. Click on "Contents" to get to the message board.
North Carolina Horse News - Fairly active forum with predetermined discussion groupings.
Ohio Horseman - This is a monitored forum. It is used almost exclusively by Ohioans to discuss items of local interest.
East Tennessee Trail Riders & Owners - This is a reasonably active board with daily postings. They also have a Tuesday chat session.
Texas area Stolen Horse Alerts
Illinois Horse Online Forum - You need to register including filling our a form with your full name and address, which is manually approved/denied. The process can take 7 days.
Breed/Type Focused Forums
All Breed and Arabian Horse Message Boards and Web Rings
Flatwalk - Very active board of people interested in soft gaited horses
Gaited Horses.Net - Website for the "Smooth Ride" enthusiast. There are several threads related to trail riding that are very active.
Gaited Horse International Association
Other Forums
Giddy Up Go -- Active horse forum, advice and discussions on everything pertaining to horses.
Google - (ATT) search results for trail rider message boards (Approx 50,000)
Yahoo - search results for horse trail ride message board (Approx 40,000)