Always experimenting with new techniques, I've become fond of using a Snoot for portraits. Using a snoot really restricts the beam of light from your flash and creates a dramatic mood in your shot. I discovered this technique by viewing photos from UK-based photographer Nick Turpin. He uses this technique for street portraits and excels at creating dramatic lighting, using only speedlights with snoots. Check out Nick's website to see what he has done with this technique.
The above photo was taken by getting a base ambient reading, then underexposing the shot by stopping down my aperture by about 2-3 stops. Then I placed my SB-800 on a stand, camera left and placed my homemade cardboard snoot on my flash. To make sure I had the flash aimed where I wanted it, I simply made sure that Jenn (my model) could see the fresnel lens on my flash through the snoot from where she was standing. Then I dialed in the flash to add as much light as I liked. Its a cool technique and easy to do. If you would prefer to have a "real" snoot as opposed to a DIY version, then check out Honl's lineup of light modifiers.