An ajax script that inserts a page into a div, or other element that supports the innerHTML attribute.
Very useful script! Just make sure to note that this uses GET and not POST so it's not the best option for submitting forms, however, it works amazingly well for updating information. For example if you have a list of products you need to sort by date, name, id or price - then you simple use this script to access a file that does the sorting for you.