I used Stone Surfaces in MD (Silver Spring) and had a very positive experience.

ABKA in Rockville, Domininion in Sterling, VA (high end), Pyramid in Springfield (budget)

Here's a link to a thread that recently discussed this topic for the MD/VA/DC area...

Here is a link that might be useful: Countertops in Maryland

After a lot of visits and comparisons at several granite companies, I gave my busines to Fairfax Marble in Merrifield, VA...they have several locations in MD AND VA as well. They have great prices, service,selection and best of all they measure, fabricate and install their product.
Hope this helps...

I also used Fairfax Marble a few years ago, with good results.

I went to Fairfax Marble and Granite in Merrifield today. They had a nice selection, and the guy was willing to give me prices by the square foot. I am leaning toward going with them.