Is there a Maven plugin that allows you to check if there are newer versions of dependencies available in the repository?
Say, you are using dependency X with versio
The VersionEye Maven Plugin is doing the same: versioneye_maven_plugin.
VersionEye can notify you about new versions on Maven Repositories, too. It is a language agnostic tool and beside Java it supports 7 other languages. Beside the simple follow/notify feature it can also directly monitor GitHub and BitBucket repositories and notify your about out-dated dependencies in your projects.

There is also a REST JSON API, for tool integrations.
By the way, I'm the dude who started this project. Let me know if you have questions.