DjZoNe

More than that, it checks if all fields filled correctly, and also makes sure to avoid comment duplication, and has flood protection capabilities as well.
Probably one of the best ways you could spice up your WordPress Blog with AJAX; readers love it! Must see for yourself.
This plugin works well in all major Web browsers, and uses discrete AJAX. 
That means if JavaScript disabled, it’s using the original comment posting method.
Ajax Comments known to work well, with Authimage plugin, but I rather suggest Akismet, as it is free for personal use.
Features:
<pre><code>* comment form validation happens server-side without refreshing or leaving the page
* Script.aculo.us Fade In/Out Effects make readers happy
* works with AuthImage captcha word verification plug-in to prevent comment spam
* still works traditionally if browsers don't support JavaScript (or have it disabled)
* uses existing theme code to match styled comment threads when producing new comments
* 25-second server timeout ensures readers aren't left hanging
* works in current versions of Firefox, Internet Explorer, Opera, Netscape, and Safari.
</code></pre>
Recommendations:
<pre><code>* perfectly compliments any well-styled comment form design-don't design without it
* best when moderation is off (seems more real-time) and AuthImage is installed (self-moderation is the best moderation)
</code></pre>
<h3>Known bug</h3>
I’ve discovered that AJAX Comments 2.0 stops working properly if you 
have ShowOnFrontPage plugin (v0.3.1) installed.
And we got another report, that it also stops, when you have SpamKarma activated.
We are working on a solution.
<h3>AuthImage Integration</h3>
<ol>
<li>Open ajax-comments.php and uncomment lines: 92, 152, 153.</li>
<li>
Open comments.php from your /themes directory and use the following code (mostly just the ids) for AuthImage to appear in your comments form:
<pre><code> <?php if ( !$user_ID ) : ?>

 <img id="auth-image" src="<?php echo get_option('siteurl'); ?>/wp-content/plugins/authimage/authimage-inc/image.veriword.php" alt="Verification Image" />
 <label for="code">Word Verification (<a href="#" onclick="document.getElementById('auth-image').src+='?'+Math.random();return false" title="Generate another Captcha Word Verification image.">can't read it? try another!</a>)</label>
 Please type the letters you see in the picture.
 <input name="code" id="code" type="text" class="text" tabindex="5" />

 <?php endif; ?>
</code></pre>
</li>
</ol>

AJAX Comments

Post comments quickly without leaving or refreshing the page.

Marc Tönsing

lefalque

Adds a link next to the reply link below each comment, which allows visitors to flag comments as inappropriate. 
A sub page to comments in admin is added, where an administrator may review all the flagged comments and decide 
if they should be removed or not.
Admins or logged-in users with comment moderation permissions are able trash or replace comments with 
one click in the frontend. This action can not be undone. A “trash” link will appear bellow all comments. 
Don’t worry: You can untrash them if until you reload. You are also able to replace the comment text with a custom 
text which can be set in the settings.
<h4>Features</h4>
<ul>
<li>Ability for visitors to report comments they find offensive.</li>
<li>Once a flagged comment has been deemed ok, it wont be able to be flagged again.</li>
<li>Flagging is done via ajax for smoother experience for the visitors.</li>
<li>Decide whether all visitors or only logged in users can report comments.</li>
<li>Trashing and Replacing with ajax in the frontend for faster moderation.</li>
<li>Fully localized. Comes with English and German translations.</li>
</ul>

MarcTV Moderate Comments

Grants visitors the ability to report inappropriate comments and admins to replace and trash them in the frontend.

AJAX Comments vs MarcTV Moderate Comments