The ones featured in this comparison are:
2. Yahoo’s YUI
There is also a mention in that comparison (although not compared) about the following toolkits
1. Kabuki AJAX toolkit from Zimbra. They have a Network and an Open Source Edition.
Just today I heard about another Framework jMaki, now this Framework too is impressive and it has integration with Netbeans and eclipse where developers can drag and drop jMaki widgets into their JSP pages. They also have some sort of integration with DOJO , YUI and GWT. Check them out.
Good luck and happy AJAXING and AJAXIFYING the WEB.