In our documentation for authoring Operations Manager management packs, we regularly reference the Management Pack Development Kit, mainly the Module Type Reference that includes reference documentation for the modules that are included in the standard Operations Manager 2007 R2 libraries. Once you know how to build a custom discovery, monitor, or rule in a management pack, then your next question is often what modules are available to provide the various logic that you need. Of course, when you find such a module you need to know how it works. While we had most of the modules documented for some time though, there were some critical modules that were not included.

http://blogs.technet.com/b/mpauthor/archive/2011/09/21/new-module-documentation.aspx