aa-globe

This plugin has no settings. 
Just activate the plugin and check if sold out items have moved to the bottom of the list.

Catalog Sorting by Stock Status – In Stock First, Sold Out Last

This plugin changes the sorting of a catalog (or product category) so that out-of-stock items are always at the end of the list

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.

Catalog Sorting by Stock Status – In Stock First, Sold Out Last vs Posts Order Widget