Van Halen-Running With the Devil (this was always my motivating song when I ran too)
As far as riding I can especially relate to the part that says "yes I'm living at a pace that kills" =)
If you want horse related songs: Wildfire(I love this one too, maybe this is my OTHER theme song), A Horse With no Name, Wild Horses, Who's going to Ride Your Wild Horses, and Rodeo by Garth Brooks. OH! And That Girl is a Cowboy also by Garth Brooks. :)
A horse is the projection of peoples' views about themselves--strong, powerful, beautiful--and it has the capability of giving us escape from our mundane existance.