WP Random Post Thumbnails
This is an official Wordpress plugin I created after needing the functionality on a client's website. I figured that I may not be the only person who needed this functionality, so why not help out other developers and Wordpress users. WP Random Post Thumbnails allows you to upload images to be used as random images for posts (or any custom post type). This plugin shows one of the uploaded images as the featured image for a post (if the post doesn't have one attached already). Useful if your theme shows thumbnails for the posts, and you don't want any posts without images.