Monkeyflowers hold a unique place in my heart as they feature prominently in plant evolution and genetics studies (including here at UM). I first learned about them there, and couldn't wait to get a few going in my own garden.
 
Purple monkeyflower is a showy tall (as far as monkeyflowers go) specimin, with vibrant pink flowers whose yellow throats attract a variety of bees. This species grows streamside at higher elevations in the Bitterroots, so down here in Missoula it's going to want some extra water. Sprinkler overspray or a sunny little spot you water regularly will do fine. 
 
It can be an annual in areas with very cold temperatures, but in Missoula this species has always resprouted for me in the spring. When in doubt, leave some seedheads and you'll be good to go. 
 
Plant with nettle-lea giant hyssop, seep monkeyflower (a low-growing yellow variety), western coneflower, and pearly everlasting.