Justin Tadlock

The Query Posts widget was written to allow users that don’t know their way around PHP to easily show posts in any way they’d like. It’s like having a cool WordPress developer as a friend ready to do your bidding. Seriously.
The widget has over 40 options to choose from. You can list posts by category, tag, custom taxonomies, author, date, time, name, or anything you can imagine. You can choose to show the full content, excerpts, or even a simple list. You can order the posts in all sorts of ways. Oh, and you can even show pages.
This is the widget that keeps users out of the code and gives them the ability to display items on their site how they want.

Query Posts

A WordPress widget that gives you unlimited control over showing posts and pages.

jeff_

Articles to Sidebar allow you to put some articles into the sidebar of pages.
When you use WP as a “normal” CMS, you could want to add some custom boxes into the pages’ sidebars. 
Whith “Articles to Sidebar” you can write articles, put them into :
<ul>
<li>a special category (in order to display to all pages)</li>
<li>a category called the same as the current page</li>
<li>both special category and category called the same as the curent page</li>
</ul>
When the article is displayed into the sidebar, the fist images it contains is used to illustrate. 
The displayed content is the article’s excerpt. If there is no excerpt, the extend (before the <code></code> tag) is used and if there is no extend, one is computed (55 first words) and used.
You can choose to put a link to the article or not. That behavior can be chanched for each articles by using a custom boolean var (articles2sidebar_display_link : 1 force link | force no link).
<h3>Versions</h3>
1 first public release 
1.1 better handling of little images ; adding the link to image when present
<h3>Translations</h3>
Actually, there are no translations, but the plugin code is ready for them.

article2sidebar

Articles to Sidebar allow you to put some articles into the sidebar of pages.

Query Posts vs article2sidebar