The IDEs whcih can develop Grails project, I use a. STS Integration 
The list of IDEs :
a. STS Integration -
Using Grails projects in the SpringSource Tool Suite, an Eclipse-based ID
I use it because SpringSource buy the G2One Inc.
b. NetBeans IDE Integration -
Using NetBeans IDE with Grails projects
I like it, too.
c. IDEA Integration -
Using IntelliJ IDEA IDE with Grails projects
Rocher said that the IDE is the most complete IDE for Grails.
d. TextMate Bundle -
TextMate Grails bundle
e. Gedit -
a TextMate like alternative for Linux
f. jEdit -
A cross platform programmer's text editor written in Java, has excellent Groovy plugin. jEdit is open source software.
g. Emacs-
GSP support for Emacs. Groovy-Mode, Grails-Minor-Mode
but, sometimes I use UE, and execute Grails's command, too :
like :
grails create-project [the project name]
grails create domain-class [the package name].[the domain object name]
grails generate-all
grails doc
grails clean
grails dev compile
grails dev war
grails dev war [the project name].war
//grails tomcat deploy
The list of IDEs :
a. STS Integration -
Using Grails projects in the SpringSource Tool Suite, an Eclipse-based ID
I use it because SpringSource buy the G2One Inc.
b. NetBeans IDE Integration -
Using NetBeans IDE with Grails projects
I like it, too.
c. IDEA Integration -
Using IntelliJ IDEA IDE with Grails projects
Rocher said that the IDE is the most complete IDE for Grails.
d. TextMate Bundle -
TextMate Grails bundle
e. Gedit -
a TextMate like alternative for Linux
f. jEdit -
A cross platform programmer's text editor written in Java, has excellent Groovy plugin. jEdit is open source software.
g. Emacs-
GSP support for Emacs. Groovy-Mode, Grails-Minor-Mode
but, sometimes I use UE, and execute Grails's command, too :
like :
grails create-project [the project name]
grails create domain-class [the package name].[the domain object name]
grails generate-all
grails doc
grails clean
grails dev compile
grails dev war
grails dev war [the project name].war
//grails tomcat deploy