sajidhussain

Instead of asking for both an email and a username on registration, this plugin lets you ask for email only, and uses that as username as well. Since the password is automatically generated and emailed to the user, this allows for sign-up form with a single form field: email.
For users that registered with different username and email address before this plugin was installed, their username and email address will be interchangeable on login.
The plugin offers a shortcode, [NP-registration], to add the registration form to a post or page.
Note: This plugin has not been tested with WP versions older than to 3.1.5. It should work with some older versions, but we can not guarantee it. However, if you are running an older version of WordPress, there are some very compelling arguments why you should consider upgrading. If you need help, there is plenty of free help to be found on WordPress.org, and Next Page, the authors of this plugin, offer a paid WordPress maintenance service.

Login Tweaks by Next Page

Use email as username to allow for single-field signup. Adds shortcode for adding registration form to post.

mpvanwinkle77

NEW FEATURES 
The Plus version of this plugin is now free! It includes reCAPTCHA, Facebook Connect, Custom Field UI, Moderation, Custom Confirmation messages. More info at http://mikevanwinkle.com/simplr-registration-form-plus/
This plugin creates a user interface for adding custom registration forms to any post or page on your WordPress website. Simply navigate to the edit page for post or page on which you would like the form to appear and click the registration forms button. A popup menu will appear guiding you through the options.
The plugin also creates an interface for adding/removing fields to be used in the registration form.

Simplr Registration Form Plus+

Easy to include new fields and custom registration forms.
Amazing Plugin.



Great Plugin

Nice plugin, this is working nice after customizing some files as my requirements.



Nice Plugin, Thanks!

The plugin uses a old form or reCAPTCHA that is no longer supported. Web links to developer are dead. There is not a lot of documentation on the shortcodes. The app has potential but needs to be improved.

Plugin not maintained

This plugin allows users to easily add a custom user registration form anywhere on their site using simple shortcode.

Login Tweaks by Next Page vs Simplr Registration Form Plus+