You can currently have an unlimited number of sidebars. Each sidebar can be called indepentenly by a shortcode and you can call more than one per post/page. Sidebars can be included in the post/page by using a shortcode like [widgets_on_pages id=x] where x is the number of the sidebar. Sidebars can also be named via the Widgets on Pages options page and that name can be used instead of the x id.

Download Plugin:

You can download Widget On Pages here: http://wordpress.org/plugins/widgets-on-pages/

Installation:

1. Install the plugin from within the Dashboard or upload the directory widgets-on-pages and all its contents to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Add the widgets you want to the Widgets on Pages widget area in the admin screens
4. Add the shortcut [widgets_on_pages id=x] to the page or post in the place where you'd like your widgets to appear (where 'x' = the id of the sidebar to use (or the name if you have named it such as [widgets_on_pages id=TagCloud]). If using only the default sidebar then no 'id' argument is needed (i.e. [widgets_on_pages]).
5. To add a sidebar into a theme you can add the following type of code to the relevant PHP theme file.
6. If you see bullet points/images next to the widget titles when using this plugin use the 'Enable Styling' setting in the options page
7. For further info check out these ace videos put together by Jessica Barnard

How to add Widgets to pages and posts: