PageLoader is a wildly customizable loading screen and progress bar plugin for WordPress.
Demo: https://codecanyon.net/item/pageloader-loading-screen-and-progress-bar-for-wordpress/6594364
DV Loading is a WordPress site preloader plugin which allows you to create a page loading animation for your site using rich set of customization options.
Demo: https://codecanyon.net/item/dv-loading-wordpress-site-preloader-plugin/17263278
Laser is a lightweight and easy to use WordPress plugin to add a page load progress bar.
Demo: https://codecanyon.net/item/page-loading-progress-bar-for-wordpress-laser/26340349