jquery is usually used as a low level js framework, the are still very many widget JS component frameworks.
What is the most popular additional library to jquery?
PS excluding jquery plugins and Jquery ui
It depends on what you need to do.
If you just want to add some other functionality to jQuery which is not in the jQuery core, such as a gallery, try googling something like:
jquery photo gallery
However, if you need to develop a fully fledged UI for a very complex web application, you should take a look at Sensha (aka ExtJS) which is targeted for such applications.