Shashank Sahu

Easy Login and Registration features with popup.
Features:
<ol>
<li>Easy to Login and Register (as modal)</li>
<li>Well customizable</li>
<li>100% responsive</li>
<li>provides sample login and registration pages</li>
<li>Compatible with all themes</li>
<li>Tested with latest WP version</li>
<li>Possible to replace wp-login.php with a custom “Login”, and “Registration” pages</li>
<li>provides after-login/registration/logout actions</li>
</ol>
Customization options:
<ol>
<li>Add plugin’s classes to your buttons to attach modal.</li>
<li>Select pages for ‘After-Login actions’ and ‘After-Logout actions’.</li>
</ol>

Wonder Login

Easy to implement login and registration by ajax .

sunnyverma1984

Increase user registration on blog by making post or page available only for registered user. 
This plugin allows to make post, page or partial content visible to registered users only. You can hide partial content using shortcode <code>[RegUserOnly][/RegUserOnly]</code>. Or you can hide complete post or page by selecting Visibility to <code>Registered Users</code> in post/page editor.
<h4>Plugin Features</h4>
<ul>
<li>Easy installation and integration</li>
<li>Custom tinymce shortcode button</li>
<li>Cross Browser capability</li>
<li>Translation ready</li>
</ul>

Only for Registered Users

Make post, page or partial content visible to registered users only

Wonder Login vs Only for Registered Users