resizable.js

resizable.js by V. Popovski. This class enables you to resize your elements, plus apply all sorts of effects

behaviour.js

behaviour.js by Ben Nolan and Simon Willison makes it possible to free your pages from “script” blocks and define a rule set based on CSS selectors to enjoy unobtrusive Java Script behaviours.

extending and overriding

Add custom behavior to script.aculo.us without altering the library code:
Howto Extend And Override

an easy example of an extension to the Effect.Base class

Use this as a template to create your own effect extensions or use the code in your own projects if you wish:
Effect Resize Extension