Both independent shops I can recommend to you are in Alexandria-
Alexandria Bavarian Service
(703) 836-2002
Martin Motorsports
(703) 823-9737
http://www.martinmotorsportsinc.com/
I've had my X serviced/modded at Martin, and the owner, Gary, is a good friend of mine. That's him waving out the window of one his many 3's on the intro page of their site. The other place is the shop that a co-worker who has a '97 3 series has been going to for 5+ years with really good result.
JV