A Joomla website's appearance is built with templates, which can be easily changed.
But building your own Joomla template is not that easy, especially if you want a Table-less design with CSS as the way to position your content.
If you are looking for free Joomla Templates, then these links below are some of the best places to start your search:
http://www.joomla24.com (English language site of Joomlaos.de)
I will be writing more on templates in the next weeks.
Below is one of the websites that offer premium Joomla Templates, extensions and Tutorials.