Eye contact. Direct eye contact is expected in the US, Finland, and France. But throughout Southeast Asia, it's best to avoid prolonged eye contact until the relationship is firmly established, or you could be considered impolite. In Latin America as well as some African cultures, prolonged eye contact from someone of lesser status is disrespectful.
The wave. Though it is common in North America to move the hand side to side, this motion can be interpreted as 'no' in Mediterranean Europe and Latin America, or as "come here" in Peru. In Greece, that same gesture is a serious insult, especially when the hand is close to the other person's face.
The handshake. A strong grip and several arm pumps to convey a message of confidence is typical in the United States. However, in Asia, the grip is often rather limp. A light lingering handshake is more favored in Latin America, and to withdraw the hand too quickly could be insulting.
Hand signals. Crossing your fingers may be for good luck in America, but in Turkey the gesture is used to end a friendship. The "okay" sign has several different meanings: in France it means zero, in Japan it's a symbol for money, and in Brazil it carries a vulgar connotation. A thumbs-up gesture that signifies "Good job!" to Americans, is considered offensive in certain parts of Australia and Nigeria.
Secret signals you may not be aware of: In many cultures, when someone taps the side of his nose with his forefinger, it signals a desire for confidentiality. However, if you see someone tapping the front of their nose in the UK, Holland, or Austria, they are telling you to mind your own business. Placing the forefinger on the cheekbone and pulling down to widen the eye signals "be alert" in Italy and Spain while in Austria it suggests boredom!