"No experience with them personally (yet) since I'm still under warranty but I've heard nothing but good things about
http://www.importmotorwerks.com/ - they recently changed their name from MPowered Automotive since they work on more than just BMWs."
I had tires installed and a four-wheel alignment by MPowered, just a few months back. They were a recommended installer at Tirerack.com. They did great work, very friendly. I was very satisfied.