dotPeek!

ILSpy is the open-source .NET assembly browser and decompiler.

JustDecompile is a stand-alone, free decompiling tool which converts assemblies into source code.

dnSpy is a tool to reverse engineer .NET assemblies. It includes a decompiler, a debugger and an assembly editor (and more) and can be easily extended by writing your own extension. It uses dnlib to read and write assemblies so it can handle obfuscated assemblies (eg. malware) without crashing.

.NET Reflector is a class browser and analysis tool for .NET. It allows developers to navigate, search, disassemble and analyze .NET components.

Created by Daniel Pistelli, a freeware suite of tools including a PE editor called CFF Explorer and a process viewer. The PE editor has full support for PE32/64. Special fields description and modification (.NET supported), utilities, rebuilder, hex editor, import adder, signature scanner, signature manager, extension support, scripting, disassembler, dependency walker etc. First PE editor with support for .NET internal structures. Resource Editor (Windows Vista icons supported) capable of handling .NET manifest resources. The suite is available for x86 and x64. »

The “Java Decompiler project” aims to develop tools in order to decompile and analyze Java 5 “byte code” and the later versions.

Zeta Resource Editor is a free application that enables you to edit standard Microsoft .NET string resources from multiple different resource files together inside one single data grid.

The MSIL Disassembler is a companion tool to the MSIL Assembler (Ilasm.exe). Ildasm.exe takes a portable executable (PE) file that contains Microsoft intermediate language (MSIL) code and creates a text file suitable as input to Ilasm.exe.

Free Zend Guard decoder, Free Java class decompiler, Free Adobe Flash swf decompiler, Free .NET (Dot NET) decompiler

GrayWolf is a .NET Decompiler that can edit the IL of a compiled .NET application. This Decompiler is targeted at hacking compiled .NET applications. This is a Beta product the IL editing is lacking and the deobfuscator is just getting going.

CFR will decompile modern Java features - Java 8 lambdas (pre and post Java beta 103 changes), Java 7 String switches etc, but is written entirely in Java 6. [ http://www.benf.org/other/cfr/ ]