I live over in Fairfax County Northern Virginia, so I have a similar climate. Here are the types of plants I have:
Every year, I buy at least one tropical annual, like mandevilla which needs a lattice. Great for privacy from neighbors and color. They can get a little expensive, but worth it for me.
Border along the pool deck=stella d'oro daylily. Months of bright yellow flowers and very little debris.
may night salvia/sage gives some nice fragrance and color from may until July.
Tall Garden Phlox lots of color late summer, many colors available
Short phlox between plants, it is evergreen ground cover with cute flowers in the early spring. I use it between plants to cut down on weeding.
Echineachea late summer color purple, doesn't take up much space
Black eye susans, lots of late summer color, gets wide after the first season
blazing star (gayfeather) tall skinny purple, the birds feed on this during the winter
Hostas are great for contracting color, but attracts slugs... nothing more disgusting than walking barefoot on one of those suckers. I have a lot, but moved them further way from the pool.
I've also added several other red hot poker plants which looks like a clump of grass, but has tall flowers mid summer (now), lavender, dahlia, strawberry yarrow, asian lilies, irises for spring color.
- - - Updated - - -
Also, nothing like leaves in the fall. I see you have a lot of trees.... I spent a fortune $$$$$$$$$$ removing all the trees on my property as they were killing me in the spring (pollen and flower litter) and the fall, insane amount of leaves to clear while waiting for my water to get cold enough to close.
