arijose

This plugin was created to stop human spammers. Captcha or other image methods do not work when an actual person is spamming your site. This plugin helps to resolve this issue. It allows your to create a custom question and answer on the registration page of a wordpress site that only the users in your demographic can answer. An example (and the reason I created this plugin) is a school track website. I would get up to 3 to 5 bogus registrations a day. I added this plugin with the question “What city is your school in?” and that number went to 0. Someone in another area is not going to know this question, however anyone who would/should be registering would defintely know the answer. This plugin will not work for everyone but it certainly was a perfect fit for me and I know it will help others too.

ARS Reg Secure

This plugin helps block bogus registrations by allowing a custom registration field and answer.

John Dalesandro

The Analytical Spam Filter plugin for WordPress blocks comment, trackback, and pingback spam. It uses multiple spam detection methods without challenging the user with obstacles such as captchas, math problems, etc. and it does not rely on external services or APIs. This is a low overhead plugin that begins blocking spam as soon as it is activated. It is compatible with caching plugins as long as the user has JavaScript enabled. The plugin blocks spam submitted through the default WordPress comment form only.
Logic is used to identify spam comment submissions. No user interaction is required. The spam blocking mechanisms work transparently behind the scenes. Most visitors will require longer than a few seconds to read a post and add a meaningful comment so any comments submitted within a short time threshold are identified as spam. Comments containing a large number of links are flagged as spam. The plugin uses an encrypted code and a honeypot to filter robotic submissions. All field names added by the plugin are randomized to prevent detection based on a source code signatures.
Configuration options include:
<ul>
<li>Enable Cache Compatibility (requires JavaScript)</li>
<li>Add spam to WordPress queue or block completely</li>
<li>Send diagnostic information to site administrator</li>
<li>Automatically compatible with the Micro Contact Form plugin to block spam messages.</li>
</ul>
Blocking options include:
<ul>
<li>Honeypot Trap</li>
<li>Randomized Internal Field Names</li>
<li>Timestamps (minimum and maximum entry time)</li>
<li>Aggressively check for excessive URLs</li>
<li>Check if JavaScript is enabled</li>
<li>Automatically block repeated spam from IP</li>
<li>Automatically block repeated spam based on content</li>
<li>Require User Agent string</li>
<li>Require Referer</li>
<li>Block Trackbacks</li>
<li>Block Pingbacks</li>
</ul>

Analytical Spam Filter

Block WordPress comment spam, trackback spam, and pingback spam through intelligent analytics instead of interactive challenge response tests.

ARS Reg Secure vs Analytical Spam Filter