Eilon's class browser for the Microsoft AJAX Library
Back in the CTP days, Wilco wrote a nice class browser that has been used for a while by the ajax.asp.net documentation site.
Eilon has written a new class browser that is more complete than Wilco's and that has the interesting particularity to build on top of a reflection layer for the AJAX library. Check it out.
http://weblogs.asp.net/leftslipper/archive/2006/11/21/ASP.NET-AJAX-JavaScript-Class-Browser.aspx