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.

KrishaWeb

Harsh Patel

Lazy Sign-In – The Smarter Way to Handle User Registration & Login
Tired of complicated login and sign-up setups? Lazy Sign-In makes it effortless to add sleek, responsive, and fully customizable login and registration forms to your website all powered by AJAX for a seamless user experience.
With just one installation, you can create both sign-up and login pages using simple shortcodes: 
[lazy_signin_ajax_signup_form] for sign-up 
[lazy_signin_ajax_login_form] for login
Why Lazy Sign-In? 
• Unlimited Custom Fields – Add as many fields as you want to your sign-up form. 
• Smart Validation – Set fields as required or unique to ensure clean, reliable data. 
• Auto-Generated Credentials – Automatically generate usernames and passwords with one click. 
• Custom Redirects – Send users to a specific page right after sign-up. 
• User Profile Management – Let users easily update their own information anytime. 
• Role Assignment – Automatically assign user roles from the backend.
The best part? Unique Field Verification. This powerful feature ensures every user detail you collect stays unique, eliminating duplicate entries and strengthening your database integrity.
With Lazy Sign-In, your users enjoy a smooth and intuitive registration process, while you get full control and flexibility on the backend. 
Bring ease, speed, and reliability to your website’s sign-up and login process with Lazy Sign-In.
Features 
• Easy installation 
• Separate login and signup pages 
• Easy customization of login and signup forms 
• Ability for add/remove fields in the signup form 
• Ability to redirect users to specific page 
• Can keep the form fields ‘required’ and ‘unique’ 
• Ability to assign roles to the users 
• AJAX verification 
• Free support

Lazy Signin

Lazy Sign in lets you easily create a fully customizable AJAX powered responsive login and sign-up form for your website.

Login Tweaks by Next Page vs Lazy Signin