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.

Dmitry Litvinov

A simple but powerful plugin with which you can show answers to the most frequently asked questions of your visitors, customers and other categories of users. The plugin displays a floating button that contains Q&A posts.

Float FAQ

Удобный виджет для расположения вопросов и ответов. Самое удивительное, что в ответы вставлять можно даже изображения! Подобных виджетов просто нет! Спасибо!!!

Floating Comments Form Fixed Scroll Position vs Float FAQ