Umm....I live in Northern Virginia so I know about the DC area. I know for a fact that there is no Walmart inside the beltway. Potomac Mills, Skyline, Springfield Mall etc all have Target but Metro doesn't go there. There are a couple of Walmarts in Alexandria. The best outlets are in Leesburg. The best place to shop is Tysons Corner, most exclusive placeto shop is Tysons II....across from Tysons I (they have good restaurants too....Cheesecake Factory and P.F. Chang).
Georgetown itself is pretty hip and chic too...esp M Street and stuff. You can take Metro to Bethesda, that's a nice place to shop too.
Hope that helps