Man greeting Man - In a casual setting, men often offer a simple nod of acknowledgment. In a more formal setting, men will shake hands. 

Woman greeting Woman - Women usually greet each other with a hello, and depending on the level of familiarity will sometimes kiss each other on the cheek or exchange hugs. In a more formal setting, women will usually shake hands.

Greetings between Men & Women- In a casual setting, a verbal greeting and/or a simple nod of acknowledgment is common.  In a more formal setting, a handshake is common.  Good friends and family may exchange a kiss on the cheek.