Buy Buy Baby (in Springfield, VA or Rockville, MD) has slings on display and you can try them. The BRU near me has some too, but mostly their carriers are Baby Bjorn types.
Oh yeah, you can at BuyBuyBaby. I've had great customer service there too trying them on. The other place I've had good success is Babies 1st in Columbia, Maryland. Also very knowledgeable staff and very willing to let you try on what you want. I bought a sling there and they helped me get the right size.
Re: Where can I try on slings and wraps in D.C. area?