ThemeShock

This lightweight plugin creates a form that is placed by default at the left of the 
content, and is fixed to the top of the page once it gets to it.
Floatin Comments serves as an alternative form to post comments that is very handy 
compared to the traditional comments form. Given that it follows you as you scroll down by 
the page, you can post a comment being at the bottom of the page but also at the 
top.
This plugin is available in 5 different languages, English, Spanish, Portuguese, 
French and Dutch, it will recognize your WordPress installation language and if 
yours is in one of the previews languages you’ll have it automatically 
translated.
<a href='http://www.wpthemeshock.com/' rel="nofollow ugc">By WpThemeShock</a> and <a href='http://www.wpthemegenerator.com/' rel="nofollow ugc"> WpThemeGenerator</a>, <a href='http://www.designshock.com/psd-text-styles/' rel="nofollow ugc">see it in action.</a>
<h3>Features</h3>
<ol>
<li>4 Different Colors</li>
<li>Fixed position when the form gets to the top</li>
<li>Ajax-Powered</li>
<li>Get 100 free sample WordPress Themes</li>
<li>5 Different languages, English, Spanish, Portuguese, French and Dutch.</li>
</ol>

Floating Comments Form Fixed Scroll Position

Floating Comments allows users to post comments to your blog through a fancy form that fallows them as they scroll down.

followalter

This plugin makes the right sidebar on post.php pages (where you edit a post) stick to the top of the screen when you scroll, so all functions of the sidebar stay within reach. It’s works with the classic version of the editor.
If the total height of the sidebar is larger than the window height, the sidebar sticks to the bottom instead, so the whole sidebar can be made visible through scroll.
On top of this, when you publish or update a page, the plugin will make the page scroll down to the previous scroll position.
This saves users from both having to scroll up (because of the stickyness) and having to scroll down again (using the previous scroll position) every time they update a post!

Admin Sticky Sidebar

This plugin makes the right sidebar on post.php pages (where you edit a post) stick to the top of the screen when you scroll, so all functions of the  …

Floating Comments Form Fixed Scroll Position vs Admin Sticky Sidebar