Jess

Thumbnail Updater does exactly what it’s name implies: it updates thumbnails. WordPress 2.9 introduced support for 
post thumbnails but one problem is that the support is not backwards compatible—meaning that if you downloaded or created 
a theme that supports post thumbnails, any images uploaded prior to the activation of that theme will not have the new thumbnail size.

Thumbnail Updater

A plugin for updating your thumbnails whenever a new thumbnail size is added with add_image_size()

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!

Thumbnail Updater vs Featured Image on Top