Karrde

Includes a file’s contents in the widget. Quick and dirty, all this does is use the PHP include function to include the specified file in the widget. There is NO checking done whatsoever on the file, so use it at your own risk. I wrote this because I couldn’t find a widget to do this ? plugins exist for using include in posts and pages, but not in widgets.

Include Widget

Includes a file's contents in the widget.

sebastianost

Usage:
To include a post in another post or page, just add [ipost id=id-of-post] and the post will apper instead of [ipost id=id-of-post]  
You can also fetch the post by permalink: [ipost permalink=”?p=4″]. 
You can also set silence to true/false depending if you want debug information to be printed. Defalut is true.(no debug information)

iPost

Plugin that makes it super easy to include one or more posts in another post.

Include Widget vs iPost