A Free AJAX Content Delivery Network from Microsoft
Microsoft's ASP.NET team has launched a free AJAX content delivery network (CDN) that will provide improved performance for your AJAX-enabled web applications.

The CDN is a network of edge cache servers around the world that stores Microsoft's AJAX libraries so your application can download necessary files faster, thus increasing web application performance.

This service is similar to Amazon's CloudFront CDN. The Amazon CDN is primarily targeted at small to medium sized businesses and developers who can't afford, and don't necessarily need, the more well-known, expensive CDNs like Akamai and Limelight. It supports the caching of images, css files, video and other static content.

Unlike Amazon's CloudFront CDN, the AJAX CDN is free for both commercial and non-commercial use and provides caching support for only AJAX libraries such as jQuery and ASP.NET AJAX.

Using the CDN is as simple as adding a couple of script elements to a page in your application that wants to access the AJAX libraries on the CDN. Also available are debug versions of the script. A single script is required to access the JQuery library.

You can get a list of the current scripts available on the CDN on the Microsoft AJAX website. Make sure you read the terms of use statement.

As libraries are updated, they will be added to the CDN.

If you are using ASP.NET 4, you can use the ScriptManager control to access the CDN. It has a new property called EnableCdn. If set to true, it will automatically request Javascript files from the CDN.

Learn more about how to use the ScriptManager control and  ASP.NET AJAX Preview 5 in Scott Gu's post introducing the new AJAX CDN.