The Sidebars & Widgets extension for the Debug Bar shows you all you need to know about the sidebars and widgets on the current page. It shows the sidebars displayed and the widgets displayed in them, and tells you whether all widgets in the sidebar were actually displayed.
This plugin allows you to analyze the behaviour of your WordPress sidebars and wigets, and is aimed at WordPress developers.
This plugin is an extension to the Debug Bar plugin, which is required for this plugin to work.
This plugin integrates nicely with Content Aware Sidebars, telling you what sidebars were replaced and merged. It is an essential plugin if you use Content Aware Sidebars with a big number of sidebars.