The new Grails Mail Plugin is really slick stuff. Very little effort has gone in to the thing so far and there is more to come but even in its current state this is really nice. More details are available at http://grails.org/Mail+Plugin but basically you get a method called 'sendMail' added to your controllers (or you could use an autowired mailService) that accepts a closure and the contents of the closure express the details of the message being sent. A simple example looks like this...
subject 'Hello Fred'
body 'How are you?'
Take a look at the docs for more information. This is good stuff already. I think the simplicity of sending a message like this is pretty impressive but more impressive is how easy it is to build support for something like that in a dynamic language like Groovy. More and more folks are taking advantage of the Grails Plugin System to easily add capabilities like this to their web apps.