I've brought my cars to Benchmark Motors off of Rt 108 on Red Branch Rd. They do a good job, but are a little on the expensive side. The owner drives an E39 528i and knows his stuff. They've done everything from putting on a coilover suspension, various exhausts, and x-brace on my E36 325is to replacing the auto tranny on my old E30 325es.
Danny is the owner and is the best mechanic there-VERY knowledgable.
(410) 730-0990
Tell them Jed with the red 325is sent you.
Another place that people have recommended to me in the Catonsville area is Urban's. I haven't been there, but a couple people have had good experiences with them.