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.
Rainbows right? Who does not like rainbows? In this Photoshop tutorial you can learn how to create a rainbow from scratch and add it to any image of your choice.
A bit longer Photoshop tutorial, but still very suitable for beginners, where you will learn how to carve a random text into human skin from scratch and make it look realistic.