I like volunteer plants.  At this time of year the most prolific volunteer is the heart-leaved wood aster.  Actually verging on an aggressive weed, it blankets whole swathes of the property.  In good years, the old tennis court and the area southeast of the house are covered in a billowing white carpet.  We are removing it from the garden proper though, spreading by running roots it will bury most other plants.

Here it is with several other volunteers: black-eyed susans, blue lobelia, and ferns; the lower picture also shows a small sprig of calico aster in the foreground, identifiable by its narrow, needle shaped leaves.