Development Tool

Intellij is my integrated development environment tool of choice!  However some may not agree with me, but its the tool I have chosen.   One issue that some have with Intellij is the cost.  Intellij is not an open source development environment, so you have to pay to play.   However in my humble opinion the cost of Intellij easily gives you a return on your investment with its productivity gains.

To date Intellij has the best Groovy and Grails support.   Eclipse via a plugin has some Groovy support, but no Grails support.   Netbeans has some Groovy and Grails support.  

One problem that you have with a dynamic language is tools support.   Since there is no "typing" its very difficult (if not near impossible) to support code completion and refactoring.  Luckily the crafty developers of Intellij have done a pretty good job in supporting code completion and some refactoring (but not as good as their Java refactoring).

Intellij has options to create all the standard Groovy and Grails artifacts.  Including but not limited to:  Groovy classes, Groovy scripts, Groovy test cases, domain models, controllers, services.  

The coolest feature of the Grails support is the domain model dependency diagram.   You can see a graphical representation on how your domain objects relate.   This diagram is very similar to an entity relationship diagram.  The diagram isn't a static picture, you can create new relationships by dragging lines between the domain objects.   Intellij then will include the appropiate code in your domain objects to make the relationships happen.  Below is an example of a dependency diagram:

If you are going to be alot of development with Groovy and Grails I would highly recommend you take a look at Intellij.