Samuel Wood (Otto)

Normally when you upload an image to a WordPress site, it creates several differently sized versions of the image automatically. Themes can define custom image sizes as well, increasing the amount of images generated on your server.
This plugin changes the way WordPress creates images to make it generate the images only when they are actually used somewhere, on the fly. Images created thusly will be saved in the normal upload directories, for later fast sending by the webserver. The result is that space is saved (since images are only created when needed), and uploading images is much faster (since it’s not generating the images on upload anymore).
“Pretty” permalinks must be enabled for this plugin to function.
Note: This plugin does not work on multisite setups, due to the way WordPress handles file serving in such situations (with ms-files.php).
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Dynamic Image Resizer

Make your images change sizes dynamically.

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.

Dynamic Image Resizer vs Responsible