Consuming Web Services With ASP.NET AJAX

Simple, clear, efficient :-)
http://www.singingeels.com/Articles/Consuming_Web_Services_With_ASPNET_AJAX.aspx

PageMethods - Ajax

Very nice article on using this powerful feature
http://www.singingeels.com/Articles/Using_Page_Methods_in_ASPNET_AJAX.aspx

ASP.NET AJAX Development Approach

Three Part series

http://dotnetslackers.com/articles/ajax/ASP-NET-AJAX-Development-Approach-Part-1.aspx

Javascript : Prototype

The 'Protype'keyword allows to add extented properties to an existing object.
Its awesome how powerful is this language.
Whatever you think about it, you have to deal with it, so master the beast ;-)
Here is an example on how to add the 'reverse' propertie to all instances
of 'String' objects
http://www.javascriptkit.com/javatutors/proto2.shtml

ASP.NET AJAX Control Development

An in depth guide to developing controls with the ASP.NET AJAX
from Kazi Manzur Rashid

http://dotnetslackers.com/articles/ajax/ASPNETAJAXControlDevelopment.aspx

Json.NET

Thanks to James Newton-King for his great library
http://www.codeplex.com/json