I was unaware of summer blooming azaleas when I was growing up. In the South, the most prominent were the Japanese evergreen variety that bloomed in spring. In my quest to find colorful, fragrant plants native to the Northeast, I discovered swamp azalea (Rhododendron viscosum).
I've added several more native American varieties since then. Ironically, my favorite, Sweet Azalea (Rhododendron arborescens), grows wild in the South. The fragrant white flowers are in bloom now. Blooms are white with red filaments. They bloom better with some sun. The growth rate is slow which I like since I want them up front and center. With a little pruning my Sweet Azaleas are about four feet after seven years. Meadowbrook Nursery is a great mail-order source for these and other native shrubs.
I bought the book, American Azaleas by L. Clarence Towe, a few years ago. Great pictures and descriptions of some native azaleas as well as good advice on growing these.
I have already picked out some new ones for next year!