This is by far the most useful tool I have come across in a while. Reflector for .NET by Lutz Roeder, allows you to analyze any .NET assembly completely. It can output the code in C#, VB.NET, IL, Delphi, MC++ and even Chrome. Give it a try and it’ll take its place in your tool-set after 10 seconds of use, guaranteed.

Note: The website currently seems to be down, but keep trying.