State Focused Forums
Tennessee Trail Riders - A social network of Tennessee trail riders and horse enthusiasts
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.
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
Flatwalk - Discussion board for 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.
Giddy Up Go -- Active horse forum, advice and discussions on everything pertaining to horses.