Originally Posted By: Yuccahead
The U.S. has a new Passport Card that can be used for land or sea re-entry into the U.S. from Canada and I believe from Caribbean cruises.

Ah, that's interesting. Oh, btw, Mexico is also a country listed. It says production started July 14, but doesn't say which year, but if it's 2008, then this is a very newly available document. Much more portable and durable than your standard passport. It could easily be slipped into your wallet like a regular credit card. Thanks for that link.