Narrowleaf Mountain Mint blooms in mid- to late-summer and attracts tons of pollinators.  Its whitish blooms are lovely, and its foliage is a silvery green.
 
Like other mints, Narrowleaf sends out underground shoots as it spreads, which can be difficult to control.  Best to plant in a sunny spot where it can spread, bring in pollinators and just look awesome.
 
It's also a great plant to keep potted, if you want to pull in pollinators but rein in the spread.
 
Fun fact: Rubbing the minty leaves on the skin has been done as a mosquito repellant.