WordPress Countdown plugin is an nice tool to create and insert countdown timers into your posts/pages and widgets.
Wp Clock Counter Plugin Super Lightweight, Fully Responsive and easy to install.
Display an animated countdown clock on your sidebar. Select from several clock designs, colors, sizes, pictures and animations. Responsive plugin, ser
WordPress Flash Countdown allows you to display a countdown on your page. Or if you have a coming soon page it will display when it will be launched.