Put it on all of the BMW forums (here, Bimmerfest, BimmerForums, etc) with a lot of pics inside, outside and under the hood. Include contact information because not everyone watching the forums has PM access. Set up a separate email for this - like [email protected] or something similarly useful that you can shut down once sold.

Craigslist if you are in a good metro area, but probably not much value if in a smaller town. Autotrader always worked well for me. Cars.com hasn't been very good, never tried the other sites. YMMV of course.