The most common ones used for landscaping are Kalmia latifolia, Rhododendron maximum and R. catawbiense. All usually need acid soil. Ledum groenlandicum is also nice but it is probably best suited for a bog.

Nice, thank you for the suggestions! Can those Rhodies handle all that sun, do you think? I had planted some rhododendrons (though not the specific ones you mentioned) there in the spring, but when the heatwaves hit the DC area this summer, they couldn't handle it :(

I guess it was the heat combined with all that sun. They weren't happy.

Well there is also Agarista populifolia 'Leprechaun' and that can handle more sun. Also Ilex glabra 'Shamrock' and Ilex vomitoria 'Nana'. But none of these have showy blooms so they might best be mixed with something deciduous or one of the other suggestions above.

Of the two, Rhododendron catawbiense should be more sun tolerant. Sounds like they will get some relief from the sun in the afternoon but it might not be enough. Other factors can come into play like soil moisture, humidity, and wind exposure. You can either experiment or select a more tolerant species like the ones esh suggested. If you do try a native rhodie make sure you give it good drainage and plenty of water for the first year or so.