Barkers Motor Works in Haslemere
I've been taking my 535d here for about a year now. The surroundings may not be as plush as the local BMW dealer, but the level of knowledge and service is at least as good (if not better).
They are honest and will only perform and charge for work that needs to be done. Their diagnostic is analytical and intensive. Last last big service I had put right a number of issues that had been outstanding with the main dealer network for a long time and felt like a new car when I got it back.
I'm taking it in for its next big service very soon, I know it will be a good experience. These guys come highly recommended by both me and several BMW owner I know.