Patroklos and I each have our favorites. I like these (in no particular order):
Jenkins (not that it's actually a SonarQube plugin )
Widget Lab (not just because Patroklos & I wrote it )
One plugin I don't have but wish I did is the Views / Portfolio Management plugin. Full disclosure: I moonlight for SonarSource, the company behind both SonarQube and the Views / Portfolio Management. But I don't get a commission.
Widget lab plugin adds some extra widgets to SonarQube. These widgets might enhance existing ones or provide different representation of the same data. The latest version of SonarQube (3.7) includes two of Widget Labs plugin widgets ( duplications and documentation ) so that's why you might get confused.
To sum up, this plugin is a placeholder for widgets that make use of existing metrics
1.Hudson / Jenkins plugin
Although Sonar analysis can be easily triggered from several build tools (maven, ant etc.) I strongly believe that its native integration with the most famous open source CI server makes itself an important part of the continuous integration / deployment practice. The configuration is extremely easy and as proposed the best practice is to trigger Sonar at night builds. Team members can track day by day software quality, automatically, without bothering when a new analysis should run.
How many times have you needed to see how much your source code has improved (hopefully) in the last weeks or months? Have you ever tried to compare basic quality indeces in a single graph? Timeline plugin integrates Google Visualization Annotated TimeLine component at project level and provides a flexible way to historical data regarding sonar quality metrics. Moreover it adds version and date milestones on visualization graph by providing in depth details about the evolution of a software project. Extremely useful for all team members ( developers, architects, testers even managers ).
3.Useless Code Plugin
It may looks similar to the Sonar Core feature named Duplicate Code, but it adds some more metrics, which I think are very useful especially for large or legacy systems. In general it measures how many lines can be removed from your code. It reports what is the number of unused private methods that can be safely removed and the number of unused protected methods exist in the code that can be removed after some more careful code examination. Finally it provides some more details about code duplication informing how duplicate lines are formed (i.e. x blocks of y lines )
4. SCM Activity Plugin
Fully integrated with several SonarQube features and screens, it collects information about the authors of each source code file so you can easily know the "creators" of the issues and drop them to the lions
5.Quality Index Plugin
Have you ever wanted to check a single number (indicator) and understand how healthy is your project? I am sure you have!! Well, the quality Index plugin is exactly what you are looking for. The plugin combines four weighted axes (complexity, coding violations, style violations, test coverage) of quality and produces a ranking between 0 (lowest) and 10(highest). Moreover it calculates a method complexity factor based on the complexity factor mentioned above. Have you ever tried to get a ranking of 10 with this plugin? I think it worths the effort! :-)
6. Sonar SCM Stats Plugin
I recently wrote an article about this plugin