It's hard to find free web2.0 templates for joomla, as you can see. One of the Joomla's problem is you need to pay to get a good template.
If you want to build a blog or just a simple website you can use Wordpress to do it. You can find at Belive Blog free premium themes for wordpress.
Check the post: blog.belive.ws/2008/03/21/10-free-premium-wordpress-themes/