If you have to create a series of cropped and consistently sized images you can save time by using the crop tool's measurements option to save many steps in your production process.

Select the crop tool and simply type in the required size in the small boxes just below the menu (highlighted with yellow on the image above). You can specify Width and Height in pixels or inches, whichever suits your needs. Now, you can simply select the area to be cropped with the crop tool. Notice that the required proportions will be forced on you helping you to find the right crop. Once you apply the crop command the image will not only be cropped, but also resized instantly.