There are a lot of options when choosing a SEF / SEO extension for your Joomla site.

SEF = Search Engine Friendly / SEO = Search Engine Optimization

You can get a list of all of the ones available on the Joomla Extentions Directory here:  http://extensions.joomla.org/index.php?option=com_mtree&task=listcats&cat_id=1803&Itemid=35

The most comprehensive review I have found is here on the Alledia blog:

http://www.alledia.com/blog/joomla-urls/