I just released my new plugin, called 'Additional image sizes'. You can download it from here. I'd like to get some feedback to see how I can improve it.
With this plugin, users can add and remove intermediate image sizes. The plugin can also make copies of existing images with these new sizes. Users will be able to use the images in their posts or use them in their theme with the use of the 'Get the image' plugin (this is the use case I had in mind mostly).