TCBarrett

This plugin requires is just the front end javascript library, the following two things to be done in support: 
1. Add the class ‘simpleajaxform’ to your form. 
2. Make sure you have the correct wp_ajax handler hook defined.
It was primarily built as an example for a blog post.

Simple AJAX Form

A simple jQuery javascript library to ajax enable forms.

This plugin will integrate AJAX commenting feature into your WordPress Blog. It uses the powerful JavaScript Framework jQuery to handle AJAX requests and jQuery Validation plugin by bassitance.de to validate comment form on the client side.
<h4>Feature Summary</h4>
<ul>
<li>Enable AJAX Commenting</li>
<li>Client Side Form Validation</li>
<li>Easily rolls back if JS disabled</li>
<li>Easily configure custom styles for messages</li>
</ul>
<a href="http://webdeveloperplus.com/wordpress/new-wordpress-plugin-wdp-ajax-comments/" rel="nofollow ugc">See plugin page for more details</a>

WDP AJAX Comments

This plugin will enable AJAX comment posting on your WordPress blog.

Simple AJAX Form vs WDP AJAX Comments