Desaturation

Desaturating the colors in some kinds of images has a unique and compelling look.  All you have to do is open the hue/saturation dialog box in Photoshop (Image > adjustments >hue/saturation) and then move the saturation slider to the left until you like the results.  In addition, you can add a significant amount of clarity (using the clarity slider in Adobe Camera Raw or Lightroom).  This introduces a gritty look that embellishes texture such as the wrinkles in this man's face.  This slider actually sharpens the midtones in the photo, but it has the effect of adding contrast and texture.  If you want to exaggerate this course, textured look, use the tonal contrast filter in Nik Software's Color Efex Pro 4.