Reflector

If you don't have this program, download it... now!

http://www.aisto.com/roeder/dotnet/

It's remarkable.

It allows you to disassemble a .NET assembly and view it's internal coding. Very handy if you want to see what makes the .NET framework tick (or any other .NET assembly).

It also allows you to view the code in several different languages. I find it very handy for translating from C# to C++.