Open-source, free Java Decompiler
Check out:
- Krakatau; the author is active on stackoverflow.com.
- CFR
- Procyon decompiler
- Fernflower and mirror
- mstrobel/procyon's Java Decompiler, actively developed
Here's a recent discussion with participation from procyon's author (BonesJustice) and Krakatau's author (Uncaffeinated): http://www.reddit.com/r/ReverseEngineering/comments/1fb1to/new_open_source_java_decompiler/