Radek Mezulanik

This plugin:
<ol>
<li>
Add 3 hidden fields to Registration form and to Comments form, that only robots can see. Plus you can choose to add validation checkbox to forms.
</li>
<li>
Add to .htaccess file direct access protection for comments file.
</li>
<li>
Check time user spent on page and time when user send a form.
</li>
<li>
Disable trackbacks for past and future posts.
</li>
</ol>
Additionally you can choose to add validation checkbox to forms.

Antispam Revolution

Three way antispam protection for registration and comment forms.

Garth Mortensen

A plugin that interacts with the StopForumSpam.com api to protect your 
website. Find out how many unwanted attempts have been blocked in Dashboard > 
Tools > Seriously Simply Spam Blocker.
<h3>Usage</h3>
Simply upload/activate the plugin and you’re good to go.

Seriously Simple Spam Blocker

A plugin that interacts with the StopForumSpam.com api to protect your

Antispam Revolution vs Seriously Simple Spam Blocker