When I wanted to have basic AJAX functionality, I searched, downloaded, tested a variety of AJAX frameworks. In the end I started using JQuery to add AJAX and other nifty interactions to the web sites I build.

jQuery is a fast, concise, JavaScript Library that simplifies how you traverse HTML documents, handle events, perform animations, and add Ajax interactions to your web pages. jQuery is designed to change the way that you write JavaScript.

JQuery.com

Above pretty much sums up what JQuery is and what it will do for you. It is easy to understand and use but if you are in a hurry and need to get certain type of interactions available on your web site, you can find a solution by browsing through the library of plugins that are readily available. In no time you would have Ajax functionality available on your web site.

Here are some of my favorite JQuery Plugins:

Tablesorter 2.0
Sean O's MP3 Player
UI Tabs

If you wanted to dig deeper and learn more about JQuery, there is a wealth of information available online including tutorials. You may also want to get the following books:

Learning jQuery

Jonathan Chaffer. Packt Publishing 2007, Paperback, 380 pages, $33.85

jQuery in Action

John Resig (Foreword). Manning Publications 2008, Paperback, 376 pages, $24.84