JReveal.Org  
   Online decompiler and obfuscator. Also has a resource directory. [Freeware]
   http://www.jreveal.org/

JODE (Java Optimize and Decompile Environment)  
   Java decompiler with full source code. Supports inner/anonymous classes. Also contains a small, but extensible bytecode obfuscator/optimizer. [Open Source, GPL]
   http://jode.sourceforge.net/

ClassCracker  
   Visual Java decompiler from Mayon Software Research. [Commercial]
   http://www.pcug.org.au/~mayon/

Decafe Pro  
   Java Decompiler for Win32 platform. [Commercial]
   http://decafe.hypermart.net/

dis  
   A functional, fast and simple disassembler that is written in C. Like javap, produces bytecode. Download Solaris, Win95/NT versions. Mac or other Unixen or source code by email request. [Freeware]
   http://www.cs.princeton.edu/~benjasik/dis/index.html

SourceTec Java decompiler  
   Patch to Mocha which defeats Crema. [Shareware]
   http://www.srctec.com/decompiler.htm

SourceAgain  
   Java Decompiler for Win95/NT, Unix, web-based trial version from Ahpah Software. [Commercial]
   http://www.ahpah.com/product.html

Mocha  
   Hanpeter van Vliet's first Java Decompiler. Orphaned at Java 1.02, so crashes on inner classes. [Freeware]
   http://www.brouhaha.com/~eric/computers/mocha.html

JReversePro  
   Decompiler/disassembler written entirely in Java. Provides facility to inspect constant pool contents. [Open Source, GPL]
   http://jrevpro.sourceforge.net/

CafeBabe  
   Graphical disassembler and editor of Java bytecodes. [Open Source] Note: download at parent page.
   http://www.geocities.com/CapeCanaveral/Hall/2334/Programs/cafebabe.html

Cavaj Java Decompiler  
   A freeware utility that reconstructs java source code from CLASS files. You can browse the reconstructed source code with the Class View for instant access to methods and fields. It uses Jad as its Java decompiling engine. [Freeware]
   http://www.bysoft.se/sureshot/cavaj/

JCavaj  
   A free Java-based Java Decompiler. It uses Jode as its Java decompiling engine. [Open source, GPL]
   http://www.bysoft.se/sureshot/jcavaj/

JADO (Java Decompiler And Obfuscator)  
   A decompiler for Java which is platform independent and has options to obfuscate the class file also. [Open source, Public Domain]
   http://sourceforge.net/projects/dcompiler

RIIS: Decompiling Java  
   Godfrey Nolan's book on writing your own Java decompiler. Early chapters are online in PDF format.
   http://www.riis.com/publications.htm

ClassSpy  
   GUI class analyser and decompiler. Also provides a simple obfuscator. [Freeware]
   http://www.psychoticsoftware.com/Products/ClassSpy/