Anthony Acosta

Provide visitors to your site the the option of increasing or decreasing the size of text by clicking on an icon which represents larger or smaller text.
Usage is simple. You can insert the code <code><?php if(function_exists('wptextsizerincutil')) { wptextsizerincutil(); } ?></code> where ever you would like the icons to appear.
NOTE: Some text will not resize if it uses an absolute size (pt) rather than a relative size in the CSS. This plugin will only resize text elements within the “content” div tag. If you are not using a div tag called “content” this plugin will not work for you.NOTE: Some text will not resize if it uses an absolute size (pt) rather than a relative size in the CSS.
All the information (general, changelog, installation, upgrade, usage) you need about this plugin can be found here: <a href="http://kennedymedia.com/wp-text-sizer" title="WP-text-sizer Readme" rel="nofollow ugc">wp-text-sizer Readme</a>.
Changes. Original code looks for the CSS “toparticle”, this has been corrected so that it searches for “content”.
<h3>Development Blog</h3>
<a href="http://kennedymedia.com/wordpress/" title="Kennedy Media's WordPress Plugins Development Blog" rel="nofollow ugc">Kennedy Media’s WordPress Plugins Development Blog</a>
Version 1.1.1 Fixes php shortform tags (Special thanks to Peter Fraterdeus for pointing this error out)

WP-Text-Sizer

Provide visitors to your site the the option of increasing or decreasing the size of text onclick of image or text links using JavaScript.

Code for the People Ltd

Scott (@scottsweb)

Test your responsive website from the WordPress admin bar. This plugin uses the excellent <a href="http://lab.maltewassermann.com/viewport-resizer/" rel="nofollow ugc">Viewport Resizer bookmarklet</a> to add a responsive button to the WordPress admin bar. Once pressed you can easily test your site in a range of common viewport sizes (e.g. iPhone, Tablet and Desktop).
The plugin is handy for testing during development and also for writers and editors to preview their content on different devices.
Banner illustration above by <a href="http://gemmagarner.com/" title="WordPress design and illustration" rel="nofollow ugc">Gemma Garner</a>.
<a href="http://scott.ee/" title="WordPress web design Hampshire" rel="nofollow ugc">a plugin by Scott Evans</a>

Responsible

I first heard about this plugin via the WordPress Plugins A to Z podcast. 
The name was catchy, so when I found myself doing responsive styling work today, I thought I'd try it out. 
All I can say, is that the interface alone makes this plugin stand out.
Responsive coding can be painful, but this plugin adds order to what can become a nightmare of manually resizing your browser window.
5 stars from me. Very nice.



Slick UI makes responsive testing more fun

Viewport resizing comes to the WordPress admin bar.

WP-Text-Sizer vs Responsible