Recently I did a few portraits of Jenn using the cross lighting technique. I really enjoy this technique as it lights your subject from both sides and all it requires is one off camera flash and available sunlight (techincally, a two light setup).
To get the shot above, I set my camera to manual, then I set my shutter speed to 1/250s because that is my fastest flash sync speed, I think (I might be able to speed it up with the D300, but haven't figured that one out just yet). Then I adjusted the aperture to get the background exposed how I wanted it. I actually used a smaller aperture than I needed to properly expose the background because I wanted it a little darker, for a dramatic look. The sun was behind Jenn and to the left so I placed my flash on a lightstand to the right and in a direct line with the sun. The flash was about 5 feet away from her and used bare at full power. There's no point in trying to diffuse the flash at this time of day because you won't get enough light on your subject due to the strength of the sun. Then I simply fired away. My flash was triggered by my D300 using Nikon's CLS mode.
For some really awe inspiring, cross lighting photography, check out the work of Brent Williamson. He is a New Zealand based photographer who has excelled at this method and has some terrific work. His blog is State of the Nation.