Cascading
Snowfire
Petticoat
Cascading and Snowfire both have a cascading habit. Cascading is not hardy here though, while Snowfire is hardy to Zone 8. Petticoat is more upright in habit and being so would also hold its own in a perennial bed. It is also hardy to Zone 8 so might be worth a try if you have a protected, moist, well-drained site. Okay so they are high maintenance but they are tauted to bloom from May to October so may be worth the extra effort. Large pots with water crystals added to the soil might be a great way to grow them. They like morning sun or light shade and they would look especially lovely growing in pots in a grove of high canopied trees. I will try them in that situation.