Squishy.js

by Chris Sauvé of lemon design

Squishy is a jQuery plugin that automatically resizes text to exactly fit the container with no extra work on your part.

You can view a demo on the project page for this plugin.

Much thanks to the guys at Paravel for their work on FitText, on which this script is largely based. This plugin only works for a single line; if you are looking for multiline text fitting, I recommend SlabText.