How to create the Google Suggest feature with ASP.NET 2.0
If you love Google Suggest, and want to learn how you can implement this same functionality in your own sites, this article is for you.

Dynamic page updates using XMLHTTP (ASP.NET)
(Microsoft Article) This is a nice detailed article about how to create a page driven by XmlHttpRequests all the way from the client to the webservice back-end.

Cross Domain XmlHttpRequests (C#)
One of the limitations of AJAX is that you cannot make cross domain requests.  This means that if you are at www.yourdomain.com, you cannot make an XmlHttpRequest to www.mydomain.com.  This article demonstrates a little work around by handling it on the sever side.

Ajax POST request (C#)
Here is a quick and simple demonstration on how to make AJAX calls using POST data rather then the standard GET.

AJAX Based Chat
I ran across this right after I finished my own AJAX chat tutorial.  I knew this would be one of the most common uses of AJAX.

AJAX Paging Control for ASP.NET
This control tutorial shows you how to page through a datagrid result set without the traditional postback.  I think most purest would complain that this is breaking the web (the back button) but I'm sure that it has an appropriate time and place.

AJAX Zip Code Lookup
I believe that one of the best uses for AJAX is preemptive form validation on fields that can't be checked with regular JavaScript.  This tutorial shows you how to lookup a ZIP code and see if it is valid using AJAX.  A very nice tutorial.