Lately I was looking for a Maven plugin to solve the problem that I want a certain Maven build to fail as soon as new duplicate classes have been introduced by other developers / third party dependencies while knowing that I already have some duplicate classes that I can't get rid of right now. Basically a duplicate classes detector with the possibility to define an exclude list - that's where the maven-duplicatefinder-plugin of Ning Inc. will give you a helping hand.
The maven-jarsigner-plugin is a pretty handy Maven plugin if you want to sign the jar file produced by your Maven artefact build. The plugins documentation does provide several examples for that use case.
But if you want to sign just some jar files in the scope of your Maven build - especially if you need to apply certain include / exclude patterns - than the documentation provides only the configuration options you have to put together to make it work. Here's an example how to sign several jar files using include / exclude patterns.