Over the weekend, the first release of the jQuery Mobile project was announced. The idea of the jQuery Mobile project is to simplify building web applications for mobile devices, in a way that provides as great an experience as possible on various complexity of devices.
This is where jQuery Mobile steps in. It is based on jQuery, and uses the principle of progressive enhancement with the goal of being functional in all HTML-capable mobile browsers. It uses HTML5 and CSS3 features in the highest end browsers and degrades well to provide interfaces for simple HTML browsers.
You can find out more about jQuery mobile on their blog, including download and CDN links.