Monkey Flower, Mimulus ringens, is an attractive, unusual plant and prolific seeder.  It will create a nice patch of purplish-blue blooms relatively quickly as long as it has moist conditions preferably in dappled sunlight. 
 
     Its small flowers bloom all summer through September, attracting butterflies and hummingbirds, although bumblebees are its primary pollinators.  Its form is narrow and upright.
 
     Monkey Flower grows naturally in swampy meadows and along pond and stream banks.
 
     Fun fact: Mimulus, in Latin, means mimic, a name Carl Linnaeus gave the plant because he thought the flower resembled a monkey's face (Cullina, W. Growing and Propagating Wildflowers of the United States and Canada).