Luigi Cavalieri

RedBrick is able to block most of the automated spam comments a WordPress blog receives daily.
It is based upon a score system that ensures spam comments are blocked as soon as possible, so as to minimise the number of checks each comment must go through. When in doubt, RedBrick always holds the comment in the moderation queue. Comments identified as spam, however, never reach the database.
As a last resource in discerning the kind of comment under examination, RedBrick takes account also of the comment author’s history.
The plugin is designed to work on low-to-medium traffic blogs.

RedBrick

Simple anti-spam plugin for WordPress blogs.

Ranjan Vilakhe

prasidhda

It is a very simple plugin to filter out the spam comments by using the popular technique called “Honeypot”. This is not the 100% solution to every possible spam comment, however I believe that this simple pattern can avoid at least 50% of spams in your comment.
<h3>Main Features</h3>
<ol>
<li>Option to user defined honeypot fields</li>
<li>Option to record logs</li>
<li>Option not to save trapped spammed comments to database (Complete removal)</li>
<li>Option to email domain restriction</li>
<li>Option to choose trapped spam comments status ( spam or trash )</li>
<li>Option to block comment with common spam words</li>
<li>Option to add your own spam words</li>
<li>Option to block comment if comment content includes any link.</li>
<li>Option to block comment from IP address</li>
</ol>

Honeypot for WP Comment

Simple plugin to trap the spam comments using honeypot technique.

RedBrick vs Honeypot for WP Comment