Topcoat
Topcoat is a very neat and clean library of CSS classes specialized in form elements: buttons, checkboxes, sliders, etc. A super easy way to make your website or app look good in minutes.
Demo/Download: http://topcoat.io/
Countable.js
As you can guess, countable.js is a JavaScript function to add live paragraph, word and character counting to any HTML element. It is very small and do not rely on any JS framework.
Demo/Download: http://radlikewhoa.github.io/Countable/
iCheck
Want super-looking checkboxes and radio buttons for your new web app? Then try iCheck, a jQuery plugin which allow you to easily customize radio buttons and checkboxes. iCheck is easy to use and comes with various skins and color schemes.
Demo/Download: http://damirfoy.com/iCheck/
CSS only responsive navigation
Responsive layouts are very popular on the web right now, and this is definitely a good thing in my opinion. Here is a downloadable and reusable responsive navigation menu, made in CSS only.
Demo/Download: http://valdelama.com/css-responsive-navigation
Almost Flat UI
Based on Foundation Framework, Almost Flat UI is a complete HTML/CSS/JS framework to build your site on. It looks really clean and professional. Definitely worth a try!
Demo/Download: http://websymphony.net/almost-flat-ui/
Chart.js
Chart.js is a dependency free, lightweight and object-oriented tool to create client side graphs. It features 6 different chart types and is very easy to use.
Demo/Download: http://www.chartjs.org/
PlaceIMG
When building websites or apps, you often need placeholder images. This very handy service generates random images at the requested size. Super useful!
Demo/Download: http://placeimg.com/
jQuery PanZoom
jQuery Panzoom is a progressive plugin to create panning and zooming functionality for an element. Panzoom supports the same browsers as jQuery 2.0 and can be used with jQuery 1.9.0+ or jQuery 2.0+.
Demo/Download: https://github.com/timmywil/jquery.panzoom/
Perfect Scrollbar
If you want to be able to create perfect looking scrollbars, then you should definitely have a look to this tiny jQuery plugin. It helps you to create customized scrollbars with no css change on any original element.
Demo/Download: http://noraesae.github.io/perfect-scrollbar/
FitVids.js
A lightweight, easy-to-use jQuery plugin for fluid width video embeds. It was built by was built by Chris Coyier and Paravel.
Demo/Download: http://fitvidsjs.com/