LynneA said:
There are many wonderful shops - widely scattered over the area - but here is a list:
http://knitting.about.com/od/maryland/Maryland_Yarn_Stores_Yarn_Shops_in_Maryland.htm
If you're going to "google" yarn stores, narrow the search to Montgomery County, MD.
Annapolis in a good hour drive from Gaithersburg and Baltimore is about an hour in the other direction.
As for stores close to Gaithersburg, So Original in Olney is good. It's my favorite LYS right now. Lana, the owner, is AWESOME!!! And she has alot of yarn to play with.
Then there is another yarn store in Wheaton, MD called The Yarn Spot. They're okay. The owner is pretty cool, but I didn't get that "welcome!!" feeling from her.
Then there is Woolwinders in King Farm... Like Cyndi said, they are PRICEY!!!!
Going further towards DC, there is another shop in Bethesda, MD. The name of the store is Knit and Stitch = Bliss. Right on Wisconsin Ave. Never been there though. Bethesda=expensive!!
The only yarn store I know of in DC is called Stitch DC. They're located in Tenley Town (Right on the Red line) at 4000 Albemarle St NW.
Hope this helps. When are you coming? There's a few of us in Montgomery County that meet together one Sunday a month. Maybe you could join us?
Dani