Easy Comment is an easy commenting system for Joomla! It will allow you to react on articles in Joomla! or certain components. Check for a list of compatible component here. It's quite easy to build in commenting into custom components. 

Easy Comment is available for the price of €15,- and comes with the following features:

• Auto comments or Tag to include Easy Comment in content
• Easy integration with custom components
• CAPTCHA to avoid spam
• Fully AJAX powered
• Exclude sections or categories when using auto comments mode
• Smilies
• Email notification on new post
• Auto publishing of posts by guests configurable
• Auto publishing of posts by users configurable
• Language file for frontend translation

The component uses Ioncube Encryption. You can find the free Ioncube Loaders here.