I have been getting a lot of questions concerning travel outside of the USA and the new passport requirements, especially for cruising. Here is the link for checking passport requirements:
http://travel.state.gov/travel/cbpmc/cbpmc_2223.html
Do not get confused on the closed loop caption under cruises. It makes it sound like you can cruise without a passport if you leave from a US port and end in the same US port. What it says is that you can travel from a US port to a US territory and back, this means travel from US port to USVI, San Juan etc... so if your ship stops in the Bahamas that is NOT a US territory and you need a Passport!!
Read it carefully!!
My biggest suggestion is get the regular passport as the passport card limits your travel, if you decide in two years to go to Europe or South America you will end up having to pay for your passport anyway, save time and money just do it the first time.
Its good for 10 years. Long enough for you to travel to some pretty great spots without worrying about getting an updated passport.
Also, keep in mind that many countries state a valid passport is good for 9 years and 6 months so renew early if close to the expiration date.
If you have any questions ask them I will get answers for you.
AnnB