Leveraging the similarities between Grails and Griffon the IntelliJ IDEA team has recently updated Maia, the EAP-accesible preview of the next major IntelliJ IDEA version, with support for Griffon. You can now manage the whole lifecycle of a Griffon application development inside IDEA.
When creating a new project, select the appropriate type of application and IDEA will create the application or plugin for you.
For an existing Griffon application, use the Import Griffon application from existing sources option on the New Project screen to get a project created.
Once your project is loaded, you get a Griffon-specific project view on the left-hand side to see your models, views and controllers nicely organized.
Feel free to make changes to the application directly from a command-line, add libraries or plugins. IDEA will pick up your changes.
One useful tip: to avoid switching the to command-line window every now-and-then, use the Control + Alt + G keyboard shortcut, which will bring up a dialog to type your griffon command and run it for you.
A run configuration for Griffon is also available, so pressing Shift + F10 will compile and run your application.
I wouldn't get far in any serious application without a sound set of tests sitting in the unit and integration test folders. IDEA can run them for you and give you an integrated test report.