I have one that just hit me one day. I was riding my old boy at an ambling walk down a dirt road in the summertime (AAhhhh, summer...), and had my eyes closed, listening to the sound of his steady hoof beats. They were pounding (plodding?) a steady rhythm, and the song just fit the tempo perfectly.. "I Will" by the Beatles. I sang it out loud and he never missed a beat.
That was 10 yrs ago and I still sing it to him whenever we walk a long stretch.