Sabaoh

This plugin will add some reCAPTCHA widget to login form, comment form, and user registration form. With this plugin, sites owners can avoid spam comment, user registration, and biting password.
Mighty CAPTCHA uses a Google reCAPTCHA technology. To work, API key pair, issued Google, is necessary.
For more information about key pair, please refer https://www.google.com/recaptcha/intro/index.html .
You can choose which form will be with reCAPTCHA widget or not. For login form and user registration form, a normal size widget is too wide. So you can choose compact widget. (but I do not like it.)
Below is characteristic of new Google reCAPTCHA.
<ul>
<li>Easy for ordinary users. They only must check the “I’m not a robot”.</li>
<li>When Google reCAPTCHA recognized an access was smell fishy, image authentication screen would appear.</li>
<li>New image authentication screen is without deformed letters, with photo images instead of them.</li>
<li>Photo images authentication is for example “choose all photos of a cat”. Easy to human and hard to robot.</li>
<li>It’s easy to use with smart phone or tablet.</li>
</ul>
Why don’t you usher it into your site!

Mighty CAPTCHA

Mighty-CAPTCHA add an authentication with Google reCAPTCHA technology to login, comment, and register form, with API keys which delivered by Google.

fergbrain

Forces new users to register additional fields. Available fields are:
<ul>
<li>First Name</li>
<li>Last Name</li>
<li>Nickname</li>
<li>AIM screen name</li>
<li>Yahoo IM screen name</li>
<li>Jabber/Google Talk user name</li>
</ul>

Force User Field Registration

Forces new users to register additional fields (such as first name and last name). Note: WordPress 2.5 or higher is definite required due to new erro …

Mighty CAPTCHA vs Force User Field Registration