In Photoshop CS6, the new version of Photoshop, you can use special cropping tool and you are done, but that doesn't mean you cannot achieve the same result with older versions.
If you are mostly using only one resample image option when resizing images, then you can change the default option to the option you are using the most.
A simple Photoshop tutorial, where you may learn how to expose an object by leaving it in color while turning the rest of the photo black and white or sepia.
