I use Park Center Automotive in Manassas Park for all of the work on my cars that I don't do myself.
I highly recommend them...they are honest and they let you into the service bays (none of this "customers are not allowed in service bays due to insurance regulations" crap). They also communicate well with customers...if you want to know why they recommend doing something they will take the time to explain it.
They'll also install used parts if you ask them to (some shops have something against using used parts).
I found out about them based on some recommendations on the Bloom's Crossing HOA website/message board.
703-330-1058 is their phone # I believe.
They're located off Manassas Drive...take 28 South, left on Manassas Drive, go past Euclid, make a left immediately after City Hall onto Park Center Ct and they are on the right.
Brian