Maphilight is a jQuery plugin that adds visual hilights to image maps.
It provides a single jQuery function: $('.foo').maphilight()
In IE VML is used. In other browsers canvas is used. Maphilight has been tested in Firefox, IE, Safari, Chrome, and Opera.
Documentation is included in the docs directory, or can be found at http://davidlynch.org/js/maphilight/docs/