You can usually catch the owner at the Courthouse Farmer's Market on Saturday mornings...that way, you can sample her cupcakes before approaching her for your special order. WARNING: Her baked goods are addictive!
I hosted a baby shower recently and ordered cupcakes from BakeshopDC, their cupcakes are sold at Murky Coffee in Arlington. I ordered lemon cupcakes and red velvet cupcakes. They were the best cupcakes I've ever tasted, everyone just loved them. Highly recommended!