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!
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!