JustDecompile is a free, full-featured .NET / C# decompiler from Telerik. It comes with many nice features such as generating a project file with source code from a decompiled assembly and the ability to search for type/member usage. Decompiled assemblies can be viewed in C# or VB.NET source code modes. Registration is currently required for download.
dotPeek is a free-of-charge .NET decompiler and assembly browser with lots of useful code navigation and analysis features.
A .NET decompiler that converts executable files (.EXE or .DLL) from Intermediate Language (IL, MSIL, CIL) binary format to high-level source code, such as C#, managed C++, Visual Basic.NET, etc.
A powerful and flexible .NET / C# decompiler that converts .NET assemblies from binary format to well-formed and optimized source code.