Google Hosts Popular JavaScript Libraries script.aculo.us, Prototype, jQuery, Dojo and more

If you've ever wanted to use a JavaScript library like script.aculo.us, Prototype, jQuery or Dojo, but you couldn't upload its files to a site or you found it difficult to manage all the different versions, Google hosts them for you.

Check it out here: AJAX Libraries API

Now if they also had Ext JS things would be good