Rose of Sharon/ Hibiscus, Rose of Sharon is the only species I know of that can withstand the Utah cold. I have seen another species here with larger blooms, but I haven't found it's name. Large bush, lots of flowers, needs full sun.
Syringa × hyacinthiflora 'Mount Baker', Lilac, zone full sun to part shade. Upright and spreading growth with bluish-green leaves that turn deep purple in the fall. Fragrant white flowers in late spring. Makes an excellent hedge.
Rhododendrons are a fantastic evergreen flowering shrub which throws of tons of blooms throughout the spring and early summer. When referring to rhododendrons being evergreen, that& in reference to the two main species planted by gardeners, which.