AivarasFX

Plugin creates widget that displays simple horizontal login. 
If theme has registered sidebar on top, widget may be used to display Horizontal login for top of the page for webpage users.
Input boxes are aligned in horizontal way, not verticaly. For blog users there is no need to open wordpress login page to login.
If blog has WP-fb-autoconnect plugin installed, widget also displays Facebook connect button and allows users to connect using facebook credentials.

FX simple LoginLogout

Plugin displays simple horizontal login for top of the page. If WP-fb-autoconnect plugin installed users may connect using facebook credentials

prontotools

zkancs

Use a simple, single shortcode to allow your visitors to login or logout depending on their current status.
The shortcode outputs an a href link for you to add in the header, footer or anywhere else on your website.
Example Shortcode:
<pre><code>[login-logout text_to_login="Login" text_to_logout="Logout" class="custom-class" redirect="/shop/"]
</code></pre>
Available Parameters:
<ul>
<li>text_to_login – The text to prompt logged-out users to log in.</li>
<li>text_to_logout – The text to prompt logged-in users to log out.</li>
<li>class – Any optional custom classes to be added to the link.</li>
<li>redirect – An optional page to redirect to after logging in/out. If not included, users will redirect to whatever page they’re on when they click the link.</li>
<li>login_url – An optional parameter that user can change the URL login page</li>
</ul>

Login Logout Shortcode

A single shortcode you can place anywhere to allow visitors to login/logout.

FX simple LoginLogout vs Login Logout Shortcode