Sir-Uli

This plugin provides a possibility to block comments based on words of a predefined list. The built-in lists of wordpress only allow to send comments to the moderation- or to the spam-queue but not to block them completely. This is remedied with this plugin, which allows to block comments based on a definable list.
Attention #1: Use wordlist with care, there is no logging of the blocked comments!
Attention #2: It will also match inside words, so “press” will match “WordPress” as well!

WU – Block comments

This plugin provides a possibility to block comments based on words of a predefined list.

Comment blacklisting works well, but what if you actually want to stop someone from even reading your blog? This plugin will take care of that for you.
It uses .htaccess file modifications to deny access to your blog from particular IP addresses (Deny from) and then follows up with an ErrorDocument 403 redirect to a URL of your choice. It doesn’t hook into WordPress, which makes it a lot faster due to no database or PHP calls.

WP-BlockYou

A plugin that can be used to block or "ban" users via their IP address from viewing your blog, and then redirecting them to a URL of your ch …

WU – Block comments vs WP-BlockYou