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.
 
 
 
This little monkeyflower doesn't mind having wet roots most or all of the time, so if you have a water feature you should add this species to the mix. Bright yellow flowers (often with reddish throats) lure in a huge variety of bees. Although touted as an annual, I have successfully overwintered it in my Missoula yard. Leave some seed heads on just in case, though. It will readily resow. 
 
 
 
Did I mention that these guys like water? I did, I know, but I want to stress this. They're kind of thirsty, especially if you have them in full sun. Plant with ferns, sneezeweed, pearly everlasting, purple monkeyflower, and mitrewort for a fun range of shapes and sizes.