A few weeks ago I wrote a post about some Reflector integration that is now part of TestDriven.NET. I have now greatly expanded that integration. When you install the latest version you will find 'Go To Reflector' buttons on Visual Studio's 'Disassembly', 'Call Stack' and 'Code' context menus. This is intended to compliment the standard 'Go To Disassembly' and 'Go To Source' buttons.
You can find this functionality in the latest release of TestDriven.NET 2.0.1761 - RC1. I will try to put up a screencast in the next few days. Enjoy!