The guys from Asp.Net Resources created a compilation of code snippets that you can use as Cheat Sheets when working with the ASP.NET AJAX Library.
I've been working with AJAX lately and i must say that this is something that anybody who is new to ASP.NET AJAX should look at. Great job ASP.NET Resources!
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.