font-size

FlowType.JS adjusts font-size based on element width. Ideally, the most legible typography contains between 45 and 75 characters per line. This is difficult to accomplish for all screen widths with only CSS media-queries. FlowType.JS eases this difficulty by changing the font-size based on a specific element's width. This allows for a perfect character count per line at any screen width.  

Font Sizer is a highly configurable, unobtrusive jQuery plugin that allows users to adjust the font size of specific area(s) of text on your website. It's lightweight, easy to configure and adds a nice bit of functionality to your blog, forum or news site.  

FitText is a jQuery plugin for inflating web type. It makes font-sizes flexible. Use this plugin on your fluid or responsive layout to achieve scalable headlines that fill the width of a parent element.