Georgetown is nice because there are a lot of unique and interesting boutiques there. I like Annie Creamcheese for vintage clothes/shoes/jewelry. Neiman Marcus' Cusp store. Intermix. And there are your typical stores like Betsey Johnson, Diesel, Zara (this one has two or three floors), Sephora, JCrew, Barneys, etc.
Friendship Heights has all your upscale department stores like Bloomies, Lord&Taylor, Saks, and discount stores like Loehmanns, TJMaxx, Filenes, Stein Mart.
U St area has some quirky shops like Junction. Just google "U St DC boutiques" or something like that.
Dupont Circle also has some boutiques, though they're more hit-or-miss like Lou Lou's (accessories), Secondi (consignment). And Metro Center/Chinatown has more typical shopping like Macys, H&M, Zara, Urban Outfitters, etc.
Georgetown is a MUST! There is a small random ethnic shop down the street from Annie Creamcheese that has a ton of random touristy stuff - you'll probably be able to find some Nationals stuff there. Otherwise, I'd check at Tysons I or Pentagon City mall.
Other nearby malls: Tysons I & II in McLean. Pentagon City in Arlington. There are a lot of shops near Chinatown (H&M, etc) in DC. Chevy Chase (along Wisconsin Ave) borderline MD/DC.
Gosh. I havent thought about the pc mall in forever. I used to work for the developer that built it while I lived down there. Soooooo long ago! I haven't really been back in ages, maybe 20 years, other than short business trips!
I'd vote for Friendship Heights. It has a good high end and bargain hunting stores. I've picked up some nice things from Filene's and Loehmanns. The rest of the stores I'm listing I love window shopping in but can't really afford!
Hu's Shoes/Hu's Wear are nice boutiques in Georgetown on M St. Ella Rue is a new consignment store on P St right off of Wisconsin Ave. I peaked in last week and they had a lot of nice clothes (I saw a Marc Jacobs bag and several Prada dresses). I also like Reiss. It's a British chain and one of their few US stores is in Georgetown.
I also love Muleh in Logan Circle/U St. They carry Mulberry! Other than though that U St is mainly vintage stores clothing wise. But there are really good bars in the area!