.NET Reflector now has a version of "Pro" that allows you to go through and debug almost any third-party assembly, including SharePoint assemblies (with the exception of confusing code).
I actually just downloaded it today and it looks really good! It integrates with Visual Studio and does not change when you switch from your own code to the SharePoint assembly code.
http://www.red-gate.com/products/reflector/index.htm
source
share