I'm very surprised by the amount of photographers I meet who are shocked to learn that we use flash in full sunlight. I know this topic has been discussed before here and other sites. Strobist remains the absolute #1 resource for those who want to polish up on your flash skills. Follow this link to read one of his lighting tutorials on cross lighting.
Shooting in the full sun can really flatten your subjects so we, as responsible technical photographers, must assume the duty to make a difference when placed in this situation by turning on a strobe :) David Hobby has initiated a good bit of discussion on this subject and while this article talks about using TTL, we also want to point out that you can use your pocket wizards with manual flash power too.
Check out David's sketch of a potential cross lighting setup.
Discussion on this photo diagram here.
Here is one of our recent attempts. Sol put a speedlight on 1/1 (full power) about 4-5 feet from subject. Triggered by Pocket Wizard. Flash is 45-60 degrees from camera's angle, pretty much an exact remake / setup of the above diagram.
photo by Sol.
Saluods,
mateo

Mateo,
Great shot. One thing I’d like to point out is the “quality” of sharpness from the flash. I’ve found a fill strobe will give you charity like your example here. I particularly like the subtle depth of field fore and aft. Excellent example of specific sharpness.
tailwinds~
mike
Very educational, thank you for sharing!
Useful and interesting. Always like your post.