The deadline for those requirements has been put ahead numerous times. As it currently stands, from the Dep't of Homeland Security:

U.S. and Canadian Citizens – Single Document Option

One of the following documents should be presented to prove both identity and citizenship.

Acceptable Documents as of January 31:

    * U.S. or Canadian Passport
    * U.S. Passport Card (Available spring 2008)*
    * Trusted Traveler Cards (NEXUS, SENTRI, or FAST)*
    * State or Provincial Issued Enhanced Driver's License (when available – this secure driver's license will denote identity and citizenship.)*
    * Enhanced Tribal Cards (when available)*
    * U.S. Military Identification with Military Travel Orders
    * U.S. Merchant Mariner Document
    * Native American Tribal Photo Identification Card
    * Form I-872 American Indian Card
    * Indian and Northern Affairs Canada (INAC) Card

* Frequent Land Border Crossers — to expedite processing into the United States, U.S. Customs and Border Protection recommends using one of the above asterisked documents.

U.S. and Canadian Citizens – Two Document Option

All U.S. and Canadian citizens who do not have one of the documents from the list above must present BOTH an identification and citizenship document from each of the columns below.

Identification Documents*

    * Driver's license or identification card issued by a federal, state, provincial, county, territory, or municipal authority
    * U.S. or Canadian military identification card

* All identification documents must have a photo, name and date of birth.

Citizenship Documents

    * U.S. or Canadian birth certificate issued by a federal, state, provincial, county, territory or municipal authority
    * U.S. Consular report of birth abroad
    * U.S. Certificate of Naturalization
    * U.S. Certificate of Citizenship
    * U.S. Citizen Identification Card
    * Canadian Citizenship Card