What does Travel insurance cover?  Well it can cover almost anything depending on when you purchase it and from which company.  Most companies will cover pre-existing if you purchase your policy immediately upon making your travel deposit or within a week or two.  This depends on the company.  You can get lost luggage coverage, missed connections, vendor bankruptcy, interruption of your trip, medical sickness, hospitalization and death coverage if a scheduled carrier goes down. 

What most people do not realize is that their personal medical coverage in the States usually will not cover them outside of the USA.  If you are in Asia or Europe and pull out the Blue Cross card, good luck.  If your traveling companion gets sick or hurt and you have to take them home, you are covered for interruption of your trip.  All of these coverage's are available if you find the right Travel Insurance company and policy.

I am ranking some of the ones that I have used personally or have feedback from other travelers that liked their travel insurance company.  Also, I am not endorsing or recommending that you buy any insurance product from the companies listed below.  I am NOT an agent and I do not have a licensed to sell insurance.  The sites listed are for convenience only and you always need to do your own due diligence before you purchase any insurance.