Responsive Text is a jQuery plugin to set font sizes responsively based on its' container width. Use jQuery responsiveText to have scalable headlines, build responsive tables and more!
Readmore.js is a lightweight jQuery plugin for collapsing and expanding long blocks of text with "Read more" and "Close" links.
Squishy is a jQuery plugin that automatically resizes text to exactly fit the container with no extra work on your part. This plugin only works for a single line; if you are looking for multiline text fitting you can see SlabText.