Addy Osmani introduces backbone.js as one part of the toolkit for building mobile JavaScript web applications. Backbone is an MVC-like framework to structure your application, simplifies server-side persistence, decouples the DOM from data, succinctly separates apps into Models, views and routers and provides synchronisation between DOM, model and collections.
As well as supporting CSS based selectors, jQuery also supports XPath expressions. This page lists a plethora of code snippets demonstrating jQuery's XPath matching capabilities.