You can get a free copy of the BMW manual here: http://www.motobrick.com/index.php/topic,2252.0.html (http://www.motobrick.com/index.php/topic,2252.0.html)
Those are made for shop mechanics. If you need something a little more descriptive and written for home mechanics then there are Haynes and Clymer manuals available. Haynes are OK but the Clymer is a little more in-depth. Between the two I'd get the Clymer.
(http://www.clymer.com/images/bookimages/485.jpg)