For a sunny spot, I like snapdragons, salvia and verbena (‘homestead’) – they can be perennial here in DC. Portulacca is also an easy care annual. You could also grow herbs and ornamental vegetables like rainbow chard and amaranthus.
Here’s a good resource for native plants http://www.nps.gov/plants/pubs/chesapeake/index.htm. I have joe pye (‘little joe’), and goldenrod (‘fireworks’) – they’ve done really well and attract lots of beneficial insects. Amsonia (‘blue star’) has great fall color.