Get passports. Its not that hard, and makes it easier when travelling. Also note that in the near future (next year I think) a passport will be required to travel to any Caribbean destination or Mexico. Might as well do it now.
From the US State Dept. website:
When will the Travel Initiative be implemented?
In the proposed implementation plan, which is subject to a period of initial public comment, the Initiative will be rolled out in phases, providing as much advance notice as possible to the affected public to enable them to meet the terms of the new guidelines. The proposed timeline will be as follows:
* December 31, 2006 – Requirement applied to all air and sea travel to or from Canada, Mexico, Central and South America, the Caribbean, and Bermuda.
* December 31, 2007 – Requirement extended to all land border crossings as well as air and sea travel.