Free Tool: ILSpy
If you miss the free version of Reflector now that Red Gate's taken it over, and if you don't appreciate the functionality that Red Gate has added to it, then ILSpy is for you.
ILSpy will decompile any .NET DLL back to either Visual Basic or C# (your choice), and provide a viewer that lets you browse the results. If you want to find out how the code behind the framework DLLs works (or if you've just lost your source code), ILSpy will let you see it. There are even a few plugins for ILSpy that enhance the basic package (and they're also free).
ILSpy doesn't provide the tight integration with Visual Studio (and Visual Studio debugging) that Red Gate's Reflector does, but -- did I mention this? -- it won't cost you a dime.
Posted by Peter Vogel on 01/08/2014 at 1:17 PM