The Grails plugins project is a SVN repo and JIRA setup to support the development of plugins for the Grails project (http://grails.org)
TestDox is an IntelliJ IDEA plugin that provides enhanced navigation and live documentation of JUnit tested code. TestDox has been developed by three comitters. It is about 4 years old and has over 10000 downloads to date according to http://plugins.intellij.net/plugin/?id=96 .
Maven Integration for Eclipse provides tight integration for Maven into the IDE. Dependency management for Eclipse build path based on Maven's pom.xml, automatic download for the required dependencies, quick search for Ibiblio repository, launching Maven from within Eclipse and much more.
Grails Plugin that deals Flex code generation by scaffolding metodology, including support for presentation and service layers
The Mojo Project is a collection of plugins for Maven 2.