A free tool to convert a compiled java .class file straight to java source code.  Provides a standalone gui version and also a plugin for eclipse.

Available at java.decompiler.free.fr/?q=screenshots/jdeclipse

In addition to decompiling class files to java source, Jode can also act as an optimizer for class files, removing debug symbols, dropping dead code, and modifying the symbol table to produce shorter names.

jode.sourceforge.net