Maven check for updated dependencies in repository

The Maven Versions plugin and it's display-dependency-updates mojo are what you're looking for:

mvn versions:display-dependency-updates

Here is what the output looks like:

[INFO] ------------------------------------------------------------------------
[INFO] Building Build Helper Maven Plugin
[INFO]    task-segment: [versions:display-dependency-updates]
[INFO] ------------------------------------------------------------------------
[INFO] [versions:display-dependency-updates]
[INFO]
[INFO] The following dependency updates are available:
[INFO]   org.apache.maven:maven-artifact ........................ 2.0 -> 2.0.9
[INFO]   org.apache.maven:maven-plugin-api ...................... 2.0 -> 2.0.9
[INFO]   org.apache.maven:maven-project ....................... 2.0.2 -> 2.0.9
[INFO]   org.codehaus.plexus:plexus-utils ....................... 1.1 -> 1.5.6
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 17 seconds
[INFO] Finished at: Fri Aug 15 10:46:03 IST 2008
[INFO] Final Memory: 10M/167M
[INFO] ------------------------------------------------------------------------

If you want to receive email notifications when newer artifacts versions are available on Maven Central you can create an account on artifact-listener and choose which artifact you want to follow.
You can either search manually for artifacts or directly upload your pom.xml.

You will periodically received notifications like this one (available in english and french for now) :