Extend your image upload functionality with JCrop. Learn to redirect the user to a crop page once they have uploaded their image and save versions of the cropped images.
Chosen is a jQuery plugin that makes long, unwieldy select boxes much more user-friendly. Learn how to use Chosen in a few different ways in this episode; Rails form builder and Simple Form.
Learn how to handle multiple models in a single form with accepts_nested_attributes_for and learn how to add and remove nested records through JavaScript.
Add full text searching using Searchkick and Elasticsearch. Here I will show the steps involved in adding this search to an existing application and a sample of autocomplete functionality.