Nassau and Paradise Island in the Bahamas are running a passport-reimbursement program for visitors who stay a minimum of two nights between January 17 and March 31. Participating hotels will cover up to four passports per room. The program is meant for new passports (those applied for between December 20, 2006, and March 24, 2007) only. Get more information about the rebate program on NassauParadiseIsland.com.
Other islands and resorts have similar rebate programs, so if you do need to get a passport (or have a brand-spanking-new one) it's worth checking to see if there's a promotion going on in the Caribbean or Mexican destination of your choice. None of these promotions will last long, and I can't think of another way to get a passport (which will be valid for 10 years) for free, so if you're planning on heading south this winter and want to save some money, it's certainly worth checking out. Do keep in mind though that getting passports is not a particularly speedy process (the State Department website claims it can take up to six weeks), and that these promotions don't cover expedite fees (for an extra $60, you can get a passport in two weeks).