Passport must be valid until a date that is at least 6 months after the date of your return trip ticket.
Passport must be in good condition - two weeks ago I saw Continental Airlines refuse to allow a man to board the flight to Belize because his passport had water stains on it. The poor guy was there with fishing rod, suitcase and three fishing buddies. He claimed that he had been all over the world with this damaged passport - airline personnel were helpful, but firm. He was assisted in finding immigration so that he could make an emergency application for a new passport - they assured him he could "probably" travel the next day. This screening occured at the gate, not at check-in.
DO be prepared with all the right papers before your trip. You do not want this to be your vacation story!