Define image cropping in new image style
There are many options to choose from in Drupal for image cropping. Here is a quick comparison.


EPSA Crop



Allows a user to choose coordinates for different presets on an image. If a user defines coordinates EPSACrop will override the Imagecache process and will set new coordinates.
Image Javascript Crop



With this one you define one or more presets in imagecache using the 'javascript crop" action, a new 'javascript crop' link appears underneath the image on the node edit screen, and the resulting popup window will display those presets. This screen shows the original image and initially applies the initial crop settings defined in the preset you select, e.g.: crop 50%-50%, center-center. However, you can then choose a different area of the original picture you want to crop, dragging an overlay box over the image, altering the size etc.
Imagefield Crop



When the user uploads an image, the image is presented inside a cropping area. A cropping box is shown inside, and the user can resize and move it. Upon clicking 'preview' or 'submit', the image is cropped and the result is saved instead of the original image.
Imagefield Focus



This module allows to scale and crop images focusing on their important portions.
Image Editor



Bring Photoshop-like functionality into your Drupal website! Create/edit any images online in the powerful and feature-rich image editors and save resulted images back to your site! This project integrates several popular online image editing services into Drupal:Pixlr editors: Pixlr Editor and Pixlr Express, Picnik, Simple HTML5 editor from Aviary: Aviary Feather, Advanced Aviary editors: Aviary Phoenix; Aviary Raven (vector editor - not working yet); Aviary Peacock; Aviary Falcon, Sumo Paint, FotoFlexer and Open-source HTML5 PaintWeb editor. 

On a side note, (this is not what you were really asking, but) anyone coming to read this post looking for similar functionality directly in IMCE can use the IMCE Crop module which adds image cropping functionality to IMCE through its UI. And for kicks, if your looking for the ability for users to be able to do manual cropping on their avatars, use Avatar Crop. Or just to force Image presets on Avatars, use Image Cache Profiles.
Manual Crop