Growing to about six inches, Galium odoratum (Sweet Woodruff) is a pretty little ground cover with bright green, star-shaped leaves that encircle stems that support small, aromatic white flowers.  Sweet Woodruff is ideal for a shady, moisture-retentive location.  I have heard a few people say that it is invasive, but I have grown Sweet Woodruff for about 30 years in various locations, and "invasive" is about the last word I would use to describe it.  It couldn't be a nicer addition to the garden; the name alone is enough to sway me.  Be sure to keep Sweet Woodruff watered in dry conditions.  Partial shade in Zones 4-8.  Quarts.