Now available are driver-license size U. S. Passport cards from the State Department.
NOTE: These are NOT useable for air travel--any other transportation mode is OK. Good for Canada, Mexico and the Caribbean.
Full info and costs at the below link:
www.travel.state.gov
Look in the upper left side for a red link.
Anticipating the question: we have Brothers who travel to Mexico by land and sea and others who may go to the Dominican Republic or even here by sea. Also, you could use it as I.D. here though there's no page to stamp--I don't recommend this useage, but mentioning it for the record.