ShinichiN

This plugin adds a widget to display furture scheduled posts list on your sidebar. You can specify how many posts to be listed.
<ul>
<li><a href="https://github.com/ShinichiNishikawa/Widget-of-the-Future" rel="nofollow ugc">GitHub</a></li>
<li><a href="http://nskw-style.com/2013/wordpress/plugin-downloads/Widget-of-the-Future.html" rel="nofollow ugc">Plugin Homepage</a></li>
</ul>
<h4>Title and post counts</h4>
In the widget page, you can specify the title and the number of posts.

Future Widget

This plugin adds a widget to display furture scheduled posts list on your sidebar. You can specify how many posts to be listed.

Adam Erstelle

This plugin allows a wordpress administrator to schedule a different theme to display on the website for holidays or special events for all visitors.
The theme will be overridden on the live site for all people who visit the site. Great for setting a Christmas theme!
If you just want to have a css file added instead of a whole theme, check out the wp-scheduled-styles plugin.

WP Scheduled Themes

Schedule a theme to display on the live site for holidays or special events. (Available from Appearance - Scheduled Themes)

Future Widget vs WP Scheduled Themes