Well you have many alternatives: http://www.showmycode.com/ .
In practice, I have found JAD to be closely precise. JD-GUI is again quite good with eclipse like code viewer.
Edit (2015): Fernflower has picked up quite some hype over last couple of years. Personally I find it to be the best. IntelliJ uses it as default from Idea13 onwards (This speaks volumes as intellij is considered cutting edge as per tooling in java world is concerned). Easiest way to use fernflower would be to drag drop .class files on intellij. In case you wish to use it from command line, then this might help.