I was experimenting a while a go and found a nice way to achieve the same colour grading effects as many professional modeling and fashion photos.
Its really simple and all you need is a RAW image handling piece of software!
Ill restrain from many screenshots as their is only like 1 step to do this, first open your file in either Photoshop, Lightroom, Aperture or similar. Next get to the Vibrancy/Saturation sliders and bring both down to zero. This will give you a black and white image, so all you need to do is slowly adjust the saturation slider until the desired effect is achieved. Play with both sliders until the image looks its best and voila!