Google released AJAX libraries API. This API simplifies acces to following Javascript libraries that will host on Google:
jQuery
Prototype
script.aculo.us
MooTools
Dojo
For example, to load Prototype version 1.6.0.2 you would place the following in your HTML:
<script src="http://ajax.googleapis.com/ajax/libs/prototype/1.6.0.2/prototype.js"></script>
Source: Google AJAX Search API Blog.