dotPeek is free .Net decompiler from jetBrains. It supports framework 1.0 to 4.0 and can decompile to C#.

Features

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

Type Hierarchy

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

*Rememberthere 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]