Future Posts Calendar
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
add_action('wp_dashboard_setup', 'fpc_setup_dashboard_widget'); in the future_calendar.php file.