I'll start ....
For warm ups, I like anything upbeat - KT Tunstall, Natasha Bedingfield, Ani DiFranco, Keith Urban, Taylor Swift, Aerosmith ....
Reining work: George Strait, Brooks & Dunn, Brad Paisley, Dixie Chicks, AC/DC, Kiss, and Bon Jovi .... off the top of my head.
Dressage work: Queen, Nine Inch Nails, Muse, Metric, and, of course, Mozart...lol.
Colts I usually stick with nothing to begin with, then start with some classical.
Lots more, I just can see programs in my head to certain tunes.
Just curious as to what other folks listen to. ;) It's hard to tell what folks are working with when they have buds in.