Passport

Passport Card
"The U.S. Passport Card can be used to enter the United States from Canada, Mexico, the Caribbean, and Bermuda at land border crossings or sea ports-of-entry and is more convenient and less expensive than a passport book. The passport card cannot be used for international travel by air."

http://travel.state.gov/content/dam/passports/marie_card.jpg http://travel.state.gov/content/dam/passports/Passport%20card%20back.jpg

References:
 * U.S. Passport Card - http://travel.state.gov/content/passports/english/passports/information/card.html