A definitive list of all COM commands is virtually an impossibility because COM components have been written by hundreds and thousands of vendors.
One way to begin to see the types of COM objects that you have access to is to use the freeware Type Library Viewer. It's an app that lets you browse every registered type library (COM library) on your own machine. You can see the objects, methods and properties with which you can interact.
You can get the program at http://www.itripoli.com/itlv.asp. Once you see a library that looks interesting you can get more information from the vendor's SDK if they have one or an included CHM file if available.
