As of Dec 31/2006 all USA persons will require a valid passport to travel to and from Canada, Bermuda, the Carribean, Central & South America excluding Puerto Rico & the US Virgin Islands.
If your travel plans takes you outside the USA after Dec 31st 2006 you will need a valid passport for re-entry to the USA.

Safe & happy travels to all.

-Mike.H

I found this online, It is from the USA NBTA website. It looks like they extended the date.

Timeline
December 31, 2006 - Requirement applied to all air and sea travel to or from Canada, Mexico, Central and South America, the Caribbean, and Bermuda.

December 31, 2007 - Requirement extended to all land border crossings as well as air and sea travel.

The original rule included a December 31, 2005 deadline, but this was removed after the postponement of the rule publication.


This website also has the rules listed.
http://www.travel.state.gov/travel/cbpmc/cbpmc_2223.html

The link above seems to be broken. This link has similar information:
http://www.learnstuff.com/the-western-hemisphere-travel-initiative/
-TBNet 12/12/2012

Jamaica - along with several other countries within the Caribbean are applying for a 2 year extension to this ruling. They should have an answer within 2 weeks.

However, let's not count on that and make sure if you are visiting us from the U.S. after January 7, 2007 you have a valid passport.

The cut-off is now 08 January except for cruise ship visitors who have a 2 year dispensation.

There's been much scuttlebutt about the inequity
but lobbying efforts have so far been to naught as
only 2 air carriers have very late in the game pressed their cause and the Caricom nations supported Chavez vs. Guatemala in the UN seat
fight so it's unlikely the U.S. Congress will
change its law, a rider to another bill this summer.