For developers sometimes we program AJAX based web applications without having a clearer picture of the methodologies or patterns that we have applied. There is a list good reference patterns available at http://ajaxpatterns.org/Patterns if you want to have a thorough understanding of AJAX.
As quoted from the website, these pattern(s) are the building blocks of Ajax applications. They are more “reference patterns” than true “design patterns”, at least from the perspective of a modern Ajax developer, who will take these technologies as a given. The patterns are included to introduce the types of technologies that are used, provide a common vocabulary used throughout the language, and facilitate a discussion of pros and cons.
And for those beginners for AJAX, it is a good read.