I have been a huge supporter and user of tools like FindBugs, PMD, Checkstyle during my day to day java development, used mostly under Eclipse, through the related plugins.
I have been also preaching about their use and I still do. So please go and install them if you have not already done so! Lately with the evolution of C.I servers most of these tools are integrated through your Continuous integration cycle, and the results are usually exposed as web pages to the developers, through a quality report. Anyway I think it is handy to use them either locally or through your building process, but use them regularly.
One more tool related to all the above, that I am going to add to my list of 'quality' weapon's is Google's CodePro Analytix. It offers lots of information that can be derived through running all the tools above and many people might find the results overlapping (compared with a Sonar quality metrics report for example).
Nevertheless, the eclipse plugin works like a charm and it is good to play around. Sometimes it is fun, to run your code through various different tools and examine all the things that are being reported back.