You can compare plans & companies at insuremytrip.com
If you are a US citizen leaving the US, you'll want health care coverage (with pre-existing conditions covered, as mentioned before) & plane medical evacuation insurance - purchased separately from medjet.com. Med evac can break the bank if not covered - $10,000 & above!
We've never had a claim, so I can't say if the one(s) we've used are good at paying!
Be careful about the $ amount you purchase. Most policies = must purchase $ coverage amount at least for the total $ of the trip. For instance, trip costs $5,000; purchase policy for $4,000 to get cheaper rate. Most policies will not cover a claim in that instance.