Currently? It's got to be Beckham. With all his endorsements, he easily makes the most money and is the bigggest celebrity. He has mass appeal across different markets - fashion, gossip magazines, modeling. He's probably on the cover of a different magazine every week. I would submit that more people around the world know who David Beckham is than any other soccer player.
Having said that, Pele is the greatest ambassador of soccer that has ever lived. He is the icon. And let's not forget his role in the movie Victory with Sylvester Stallone.