As of June 1, 2009 crossing the Canada/US border will require a passport or other form of secure ID. Currently, this is the case for travelers arriving by air and now it will apply to everyone whether traveling by bus, train, ship or car.
All travelers coming from Canada, Mexico, the Caribbean and Bermuda will have to show a passport or suitable alternative which have been limited under the new rules to passport cards, new enhanced driver's licenses and Trusted Traveler Programs cards, such as NEXUS, SENTRI and FAST to enter the U.S.A. The new rules are part of the Western Hemisphere Travel Initiative.
Passport cards issued by the State Department cost $45 for adults. Because the card is only useful for US borders and NOT valid for air travel, it's wiser to spend the money on a regular passport.
As the new enhanced driver's licenses from both Canada and the US with added security features such as radio frequency identification are slow in coming they are not an option for those traveling in the near future.
U.S. citizens ages 18 and under traveling in school groups or other organizations will still be able to enter the U.S. with proof of citizenship alone. Individual children traveling with parents however will require a passport or other secure ID.