dotPeek is free .Net decompiler from jetBrains. It supports framework 1.0 to 4.0 and can decompile to C#.
Opening and Browsing Assemblies
Viewing the Source Code with Syntax highlighting and code insight (Visual Studio look-and-feel)
Quick jump to a specific type, assembly, symbol, or type member
Navigation and Search
Overview of inheritance chains
Searching in Decompiled Code
Downloading Source Code from Source Servers
Complete keyboard support
This is a really good decompiler tool which can help you to recover your code if you lost your code and have only the compiled dll.
Read more and Download dtPeek decompiler for .Net for free
*Remember there is no final version available as of now, what you can download is pre-release builds of dotPeek. The pre-Release may have bugs, and see what they says
Try the latest build, but remember that we don't perform extensive testing before publishing the bits here, so they might not work or even harm your computer.
[Via Geeks with Blogs]