Bentley Publishers has finally released a service manual for the 2006-2009 BMW 3-series models that covers the 335i and 328i convertibles. If you are not familiar with these books, you should be. Bentley makes some great books for the do it yourself mechanic.
If you are not so daring as taking on the projects yourself, the books are great for understanding what is being done to your car if you hire the work out. Also, I find these books to be a great resource to help diagnose problems and use for routine maintenance.
The price is a bit steep at $81.87 right now on Amazon.com, but at over 1,200 pages it sounds very comprehensive. more.