Sencha Touch 2 is a high-performance HTML5 mobile application framework. It’s built for hyper fast speed and responsiveness and is the only framework that enables developers to build impressive apps for iOS, Android, BlackBerry, etc on both Mac OS and Windows system.
jQuery Mobile is dedicated for HTML5 mobile device platforms, built on the jQuery and jQuery UI foundation. It has lightweight code library and flexible theme customisation.
iUI is great for building websites/web apps with mobile UI elements/touch gestures on multiple mobile platforms.
JQTouch now is a part of Sencha and used as specific jQuery plugin for mobile web development. It is suitable for small screen devices which claimed in Sencha blog.
XUI is a super tiny library if you just want some simple DOM manipulations, events handling and animations. It’s only 4.2k.