A WordPress plugin/widget that gives you the ability to put content (posts and custom post types) in your sidebar.
The Post To Sidebar plugin makes it easy to display post content in the sidebar areas of your site. Once the widget is activated, a multi-select dropdown of all your published pages appears on post editing screens. Select the pages upon which you want the post to be displayed and the post will appear on those pages.
There are options to hide the post title in the output and to show the content as an excerpt.