I've just successfully configured a continous integration build of my new grails web application using travis-ci.org.
Travis-ci.org is a continuous integration service for the open source community. It is free to use and fully integrated with github. It supports multiple programming languages including java and groovy.
To get started with travis-ci.org log in using your github account and read the getting started tutorial.
Once you have activated your github repository you need to add a .travis.yml file to your repository containing the necessary build configuration settings for travis-ci to build your application.
For a grails application you can use the following .travis.yml configuration:
Thanks to berngp@github for publishing gist!