w3prodigy

This plugin changes the internal WordPress script queues for the following AJAX Libraries: jQuery, jQuery UI, Prototype, Scriptaculous, MooTools, Yahoo! User Interface, Dojo, SWFObject, Ext-Core, Chrome Frame and WebFont Loader.

Google Hosted AJAX Libraries

Change the internal WordPress scripts to use Google Hosted Scripts

Serge Boyko

This plugin makes it dramatically easier to enqueue scripts and styles. 
Manage it from a separate option menu page.
You can enqueue in <code>head</code> or in <code>footer</code>, enqueue in admin dashboard, enqueue only for homepage, 
enqueue for all pages/posts/categories/archives or enqueue for a specific page/post/category.
Choose from any script/style in theme folder or from a specific plugin folder.
It has never been so easy before!

WP Enqueue

This plugin makes it dramatically easier to enqueue scripts and styles. Manage it from a separate option menu page.

Google Hosted AJAX Libraries vs WP Enqueue