ReflectionMedia

This plugin allows sorting of posts alphabetically, by Post Title (ascending or descending) or Post Date (ascending or descending), customizable for each category.

WP Post Sorting

This plugin allows sorting of posts alphabetically, customizable for each category.

LordPretender

This plugin adds a drop-down list with the ability to sort your blog posts :
<ul>
<li>by title</li>
<li>by date (newest to oldest)</li>
<li>by date (oldest to newest)</li>
<li>sort by date last modified</li>
<li>randomly</li>
</ul>
You can find a demo here : http://www.spoils.fr/ 
The widget is named “Trier les articles” on the sidebar.
<h3>Configuration</h3>
<ul>
<li>Widget title: the title of the widget</li>
<li>3 checkboxes in order to display or not items in the drop-down list.</li>
</ul>
Since the version 2.0.0, it is now possible to change the default order for your categories. 
In the category editing page, you will now find a dropdown list.

Posts Order Widget

Add the ability to sort the posts by context rather than descending date.

WP Post Sorting vs Posts Order Widget