We've discussed this before and perhaps the information would be very beneficial in answering your questions.
Check it out; Travel Insurance vs Travel Protection
I agree with everything Trip said, but be careful with using insuremytrip.com. While the information can be helpful, keep in mind that best price is not always best deal and biggest name does not mean best policy. The customer service provided after the sale is the most important thing and we've fired some big name companies because they did not provide good customer service to our clients.
So talk to your agent as they will usually have a company they work with and trust to provide a good product at a good price.
But do NOT purchase the insurance through the cruise line.
Let us know if you have any questions.