Janar

With this plugin you can add extra HTML or just plain text when posting a new page or post. That content will be displayed in sidebar widget. It is tested from WP 2.6 to 3.0.1.

ax-sidebar

With this plugin you can add extra HTML or just plain text when posting a new page or post. That content will be displayed in sidebar widget.

Johan van der Wijk

The <a href="http://www.vanderwijk.com/wordpress/wordpress-custom-post-widget/?utm_source=wordpress&utm_medium=website&utm_campaign=custom_post_widget" rel="nofollow ugc">Content Blocks</a> allows you to display the contents of a specific custom post in a widget on in the content area using a shortcode.
Even though you could use the text widget that comes with the default WordPress install, this plugin has some major benefits:
<ul>
<li>The Content Blocks plugin enables users to use the WYSIWYG editor for editing the content and adding images.</li>
<li>If you are using the standard WordPress text widgets to display content on various areas of your template, this content can only be edited by users with administrator access. If you would like non-administrator accounts to modify the widget content, you can use this plugin to provide them access to the custom posts that provide the content for the widget areas.</li>
<li>You can even use the featured image functionality to display them in a widget.</li>
<li>The Content Blocks plugin is compatible with the WPML Multi-Language plugin and automatically shows the correct language in the widget area.</li>
<li>The Content Blocks can be included in posts and pages using the built-in shortcode functionality.</li>
</ul>
This plugin creates a ‘content_block’ custom post type. You can choose to either display the title on the page or use it to describe the contents and widget position of the content block. Note that these content blocks can only be displayed in the context of the page. I have added ‘public’ => false to the custom post type which means that it is not accessible outside the page context.
To add content to a widget, drag it to the required position in the sidebar and select the title of the custom post in the widget configuration.
Includes the following translations:
<ul>
<li>Swedish (sv_SE) by <a href="http://krokedil.se" rel="nofollow ugc">Andreas Larsson</a></li>
<li>Spanish (es_ES) by <a href="https://www.ibidemgroup.com" rel="nofollow ugc">IBIDEM GROUP</a></li>
<li>Portuguese (pt_BR) by Ronaldo Chevalier</li>
<li>Polish (pl_PL) by Kuba Skublicki</li>
<li>Dutch (nl_NL) by <a href="https://vanderwijk.nl" rel="nofollow ugc">Johan van der Wijk</a></li>
<li>Czech (cs_CZ) by <a href="http://jsemweb.cz/" rel="nofollow ugc">Martin Kucera</a></li>
</ul>
<a href="https://translate.wordpress.org/projects/wp-plugins/custom-post-widget" rel="nofollow ugc">More translations are very welcome!</a>

Content Blocks (Custom Post Widget)

I was looking for something like this that goes perfectly with page builder based on widgets. Easy to use, simple and gets the job done.

Simple and effective

This plugin enables you to edit and display Content Blocks in a sidebar widget or using a shortcode.

ax-sidebar vs Content Blocks (Custom Post Widget)