My first published script on the Groovy Web Console!
The Groovy web console lets you run Groovy scripts without having to install Groovy. It also maintains a script library: http://groovyconsole.appspot.com/ and runs on Google App Engine.
A new GDate class with a toString() method that prints the date using the ISO 8601 format with the T replaced by a space: yyyy-MM-dd HH:mm:ss.SSS
It comes with unit tests; are you able to come up with a leaner/groovier implementation?