Photoshop CS6 now has a completely nondestructive Crop tool. When you choose the Crop tool, you will notice the new crop marquee, with eight handles instead of four. The benefit of these new handles is that we can now resize non-proportionally. The most important thing about cropping is to de-check Delete Cropped Pixels. This enables you to choose Image > Reveal All later on to undo the crop.
You can choose Rule of Thirds overlay, CS6 lets you preview Golden Ratio (a relationship between two numbers), Diagonal, Triangle, and Golden Spiral overlays. Perspective Crop helps you straighten images.
Straighten (which was part of the Ruler tool in CS5) is now a feature of the Crop tool. Click on the Straighten icon on the Control bar while on the Crop tool, and drag along the line of the image that needs to be straightened. The Crop tool automatically rotates the image and applies the crop.
You will notice that when you drag the Crop tool, the image shifts in the opposite direction. If you would like to disable this, from the Crop Preferences on the Control bar, de-check Auto Center Preview. You can even take it back to Classic mode if you don’t like the way the Crop tool has changed. From the Crop Preferences, you can also change the color of the area that is being cropped away.
Perspective Crop Tool
The Perspective Crop tool enables you to align objects as you crop with a flexible marquee. This was available in CS5, but not very intuituve as it being its’ own tool as it is now.
The best way to begin is to align the Perspective Crop marquee up with something that it’s very clear where the edges are. Like the Distort tool, you can drag each corner independently to make a skewed image appear straight-on or flat.