WP SmartCrop is a free WordPress plugin that fixes one of the biggest drawbacks of the Media Library: cropping.  However, it goes far beyond optimizing your cropped thumbnails, to make static cropping a thing of the past.

WP SmartCrop fundamentally changes how images work on your site.  Once installed, you can start using styles like 'width', 'height', 'max-width' and 'max-height', without having to worry about stretching your pictures or cropping out the main focus of the image.  All images will automatically crop, on the fly, to meet your design's needs.