In the Before Times, I bought annual medical and medivac insurance for international travel. I 'self-insure' for domestic travel--for example, paying a little more per day to have cancellation rights at hotels instead of the absolute lowest prices. If I were taking a cruise or any other high-priced travel itinerary which doesn't allow cancellation and refund, I would absolutely get travel insurance, and I'd read the fine print on what is covered and what is not.
Squaremouth and insuremytrip are good websites for quotes. Unfortunately, consumer reviews aren't very helpful. The majority of reviews say something like "Easy to purchase online. Luckily I didn't have to make a claim." I try to use companies that do business in a lot of states, which suggests that a number of different insurance commissioners have approved them.