sander85

This plugin allows to block spammers with the following options:
<ul>
<li>Block spammers by IPs (supports wildcards).</li>
<li>Block IPs that have posted comments marked as spam.</li>
<li>Block comments that contain bad words.</li>
</ul>
Additional options:
<ul>
<li>If comment contains bad words, add the spammers IP into the blacklist.</li>
<li>When deleting spam, add IPs of spam comments into the blacklist.</li>
<li>Similar entries in the blacklist are merged automatically.</li>
</ul>

Block Spammers

Block spammers from submitting comments, by IPs or by bad words.

Aleksei Znaev

This is a spam IP blocker. It is free. It marks any new comment as spam automatically when commenter’s IP exists in at least one of ‘.zen.spamhaus.org’ & ‘.bl.spamcop.net’. 
Plugin is based on public DNSBL class. 
<a href="http://www.phpclasses.org/package/6994-PHP-Check-spam-IP-address-in-DNS-black-lists.html" title="DNSBL class on PHPClasses.org" rel="nofollow ugc">Official page of DNSBL class on PHPClasses.org</a>

Spam IP Blocker

Free spam IP blocker according to public DNSBL bases.

Block Spammers vs Spam IP Blocker