Boone Gorges

Requires WordPress 3.0+ Network Mode.
Allows blog administrators to add multiple users to blogs at a time, using only a list of email addresses. When the specified email address matches an existing account, the account will be added as a user on the blog. Otherwise a new account is created and the new user added with the specified role. Based on DDImportUsers.
The plugin determines username automatically from the email address. For example, the email address bgorges100@example.com will produce the email address bgorges100. For that reason, this plugin works best when used in schools or organizations with official, unique email addresses.
When BuddyPress is installed, the welcome email will also include a link to the new user’s Edit Profile screen.
This plugin was developed for Blogs@Baruch of Baruch College’s Bernard L Schwartz Communication Institute. http://blsciblogs.baruch.cuny.edu

Simple Import Users

Allows blog administrators to add multiple users to blogs at a time.

llavillaccama

The Add new recaptcha google plugin allows you to implement a super security REcaptcha form into web forms. It protects your website from spam by means of math logic, easily understood by human beings. 
This captcha can be used for login, registration, comments forms.
This plugin is based on the recapcha of google, for receive more information can visit the website: https://www.google.com/recaptcha
<a href="http://webdesignjc.com/recaptchawp/index.html" rel="nofollow ugc">Support</a>

JC Recaptcha

The Add new recaptcha google plugin allows you to implement a super security REcaptcha form into web forms.

Simple Import Users vs JC Recaptcha