Simon Willison blogs about how JQuery won him over. From its faddish start based around CSS selectors (getElementsBySelector), and method chaining, Simon now sees the library in a new light. Simon shows how jQuery supports modern development best practice such as namespaces, giving a quick nod to the richness of jQuery selectors (DOM, CSS and XPath). JQuery's event handling looks natural and offers an event when the dom is ready. It exposes custom events for non-trivial Ajax requests. Simon's so convinced about jQuery that he's willing to overlook his rule that developers should know how a library works before using it.
Joe Hewitt, in this Dr Dobbs article talks about using the Firebug extensions to inspect and debug Ajax applications (or any browser-based JavaScript application). It also has CSS inspecting capabilities, editing JavaScript on the fly, inspecting HTTP request and responses, logging, breakpoint debugging and profiling. A useful howto.