As Trip has mentioned, alot of people use insuremytrip.com as a site to show travel insurance.
However, I warn you, be VERY careful when looking at the companies. Yes, you definitely want to compare coverages, but as I mentioned earlier; best price is not always the best deal. And biggest name is not always the best company.
For example, our company, Cruise Planners (which has over 900 agents nationwide), had 5 insurance companies we did business with years ago. It did not take long before we fired 3 of them because their customer service was lousy. (I won't mention specifics, but these were some of the biggest names in the industry.) Just because they have a big name and sell a good product is one thing, but it's the service they provide if you need to file a claim that is the biggest measure of how good a company is.
So my best advice, after selling travel insurance for over 11 years, is to work with your agent. They usually have companies they use, know, and respect. Their knowledge and experience can be invaluable when it comes to travel insurance. Plus, it gives you someone to personal deal with should you have any questions or problems. As we all know, dealing with large corporations, such as insurance companies, is not one of our greatest pleasures in life!
And I know I've said this before, but because of its importance, it requires repeating; make absolutely sure you are getting travel insurance and not travel protection. There is a huge difference between the two, the main one being that travel protection is not regulated by your State's Insurance Commission.