Derrick Tennant

It may be my personal preference, but I really like having the “Featured Image” metabox up at the top of my screen. I use it almost first thing on every post I write, so I don’t like searching for it. This plugin will force that metabox on top for the “post” post type. 
There’s only one option available, in the regular Media Settings page. “Allow Users to Customize Order” which is ON by default, can force users (if off) to have their “Featured Image” metabox stuck to the top.
Feel free to contact me, emrikol@gmail.com, if you have any problems or questions.

Featured Image on Top

Tired of having to move your "Featured Images" metabox to the top?  I've got a fix for that!

Brianna Deleasa

This plugin allows you to upload a set of images via a settings page to be shown for posts without images. The images will be chosen at random on page load for any posts without a featured image (meaning each time the page is reloaded another random image will be chosen). Useful if your theme shows thumbnails for the posts, and you don’t want any posts without thumbnails.
UPDATE: Now you can select images specifically for certain post types as well as taxonomy terms.

WP Random Post Thumbnails

Allows you to select images to be shown at random for posts without a featured image.

Featured Image on Top vs WP Random Post Thumbnails