DBanner is an OpenCart extension that allow user to custom size banners inside the panel. DBanner is based on the gridster.js. Gridster is a jQuery plugin that allows building intuitive draggable layouts from elements spanning multiple columns. You can even dynamically add and remove elements from the grid. It is on par with sliced bread, or possibly better. The extension is also reponsive.
Demo preview: http://demo.dulesan.com
Admin demo: http://demo.dulesan.com/admin
user: demo
pass: demo