Jan_J

For some wordpress themes it is very useful to limit comments to a certain amount of characters. WordPress does not offer such an ability therefore I wrote this small plugin to limit the length of the comments.
Based on: 
* <a href="http://yoast.com/wordpress/minimum-comment-length/" rel="nofollow ugc">Minimum Comment Length</a>.

Maximum Comment Length

Check the comment for a set maximum length and disapprove it if it's too long.

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.

Maximum Comment Length vs Uber reCaptcha