Almost all of those images have seen significant retouching using so-called "high end" techniques, particularly frequency separation, dodging and burning, colour grading and high-pass sharpening. There are a huge number of tutorials on YouTube for each of those techniques (with varying degrees of quality, both of the tutorials themselves and the retouching skill of the poster). Some of the better ones are by Jonas Wendorf, Michael Woloszynowicz and, if you can find them (speaking Spanish helps a lot) Natalia Taffarel. You will find many additional tuts in the "related videos" sidebar. (Please note: Woloszynowicz's work has slipped into the "obviously retouched" category lately. His dodge and burn work to reshape faces is quite artificial-looking, but the techniques he uses are still very valid. You just need to know how far to go.) (Many of the images seem to have been taken from the ModelMayhem "Challenges, Contests and Samples" retouching thread, where you can find all sorts of raw images to practice on.)

Still, all of the images started with a shot that was very good. Lighting and control of focus/depth of field are critical starting points, otherwise you're left with the task of creating what is really just a painting based on a photographic reference.