Aaron Butacov

It adds a simple month-by-month calendar that shows all the months you have future posts for (and the current month no matter what), it highlights the days you have posts for, and as an added bonus if you click a day, the Post Timestamp boxes change to that day, month and year.
Also includes a widget so you can show users what upcoming posts you have on your website.
If you want to ad a widget to your dashboard, uncomment the line <code>add_action('wp_dashboard_setup', 'fpc_setup_dashboard_widget');</code> in the future_calendar.php file.

Future Posts Calendar

This plugin adds a monthly calendar that shows all the dates you have future posts.

Aaron D. Campbell

Upcoming Posts Widget acts very much like the recent posts widget, but displays 
scheduled posts instead of published ones. Requires WordPress 2.8+
You may also be interested in WordPress tips and tricks at <a href="http://wpinformer.com" rel="nofollow ugc">WordPress Informer</a>

Upcoming Posts Widget

A widget that displays a list of scheduled posts.

Future Posts Calendar vs Upcoming Posts Widget