Door: kelbytv.com/photoshopkillertips/
Using a gradient style to adjust the sky in a photo.
http://kelbytv.com/photoshopkillertips/2010/05/07/fixing-skies-with-layer-styles/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+PhotoshopKillerTips+%28Photoshop+Killer+Tips+%28Video%29%29