AA Callister's is (or at least used to be; I moved away from Utah in 2009, so obviously haven't been for a while) a good place for that type of stuff. There's a small English section, big Western/roping section, and a good bit of horse care stuff. I always thought their prices were pretty fair. Sometimes they have the English stuff on crazy good sale.
Some nights I stay up cashing in my bad luck; some nights I call it a draw. -- fun.
Yep, Callisters is the main place around here. In Draper there's a small store called Horse Crazy that has mostly English tack and clothing as well as some decorative items. They're small but there are bargains to be found in their upstairs used section.