Chaika88

WordPress plugin to create a tree of comments on the basis of standard functions.
Plugin TWC-Templates-WP-Comments loads the template to display the comments instead of the standard WP or regular file comments.php
The plugin has a built-in spam protection, which eliminates the automatic comment spam to 99%. 
With modified AntiSpam for comments in version 0.2

TWC-Templates-WP-Comments

Plugin for creating tree wordpress comments with spam protection and unfolding responses

WP Chill

Silkalns

Cristian Raiber

A very useful plugin for everyone using WordPress. Adds reCaptcha security to the WordPress login form, register form and comment form. This plugin could help your blog get rid of a lot of spam comments or brute-force attacks.
Nothing gets passed it if the reCaptcha doesn’t validate.
A few notes about the plugin:
<ul>
<li>Supports audio or image captcha types</li>
<li>Can generate the reCaptcha image / audio type in a number of predefined languages</li>
<li>Adds reCaptcha protection to the WordPress login form</li>
<li>Adds reCaptcha protection to the WordPress register form</li>
<li>Adds reCaptcha protection to the WordPress comment form</li>
<li>Adds reCaptcha protection to the WordPress recover password form</li>
</ul>

Uber reCaptcha

This plugin adds the reCaptcha form to the WordPress login form, recover password form, register form and comment form.

TWC-Templates-WP-Comments vs Uber reCaptcha