Lutz Roeder’s .NET Reflector has to be one of the most useful tools in my bag of tricks - the ability to spelunk into the depths of an assembly to answer a tricky question has value beyond words.
Better yet, Reflector has a plug-in architecture, allowing others to extend the tool in new directions.
SequenceVIZ is one of those plug-ins, generating UML style sequence diagrams to illustrate the behaviour of a method.
Check out this example from my own code:
A couple of caveats do apply, however. Firstly, the plugin is dependent on a couple of third party extras that you’ll need to install as well - a GPL library to generate SVG files, and an IE plugin to view them.
Even so, well worth the effort.