DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
Commento - A fast, bloat-free comments system to foster discussion on your website
Commentbox - Commentbox is a jsf component that allows quick realization of a comment functionality
JLex Comment - JLex Comment is a comment system for Joomla.
HTML Comment Box - HTML Comment Box widget for your website. Copy the HTML code and it just works!
SolidOpinion - SolidOpinion is a fun, new and dynamic commenting platform.