In a recent discussion on the Joomla forum, I was referred to a thread on how to make custom "thank you" pages to be shown after a person submits a "contact us" type of message using the Joomla contacts component.

This requires some hacking of the core files, but it is pretty straightfoward and seems to work very well.

If you need this type of thing, you can find the full discussion (with source code and instructions here): http://forum.joomla.org/index.php/topic,35582.0.html