The BMW communit is vast. There are numerous sites and forums that are very helpful. Here are a few that we have found helpful.
mye28.com All things E28. One of the best resources on the web. An excellent place for E24 owners as well.
bmwe34.net A must for E34 owners. This is a collection of excellent technical information.
bimmerforums.com Forums organized by model.
bmwe21.net An excellent resource for the E21. This is an international community.