Hypericum (Rose of Sharon) are tolerant of all soils and love full sun. It is low growing and takes over an area very quickly. Bright yellow flowers. A nuisance in some areas as it takes over, but ideal for what you need.
periwinkle (vinca) is pretty everything tolerant ground cover but only about 4 to 6 in tall. Shiny green or variegated leaves and profuse blue or white flowers