Health Insurance/Accident Cover for many Countries??
 

I'm looking for any information on getting health insurance/accident cover for myself. I've been on the road in South America for 6 months now, and I've got a year left in my trip, to go up through Central America, the States and Canada, and I'm wondering is there any company that will insure this type of trip as regards health??
I've been too long without any sort of insurance now and want to get some before my luck runs out... There are a lot of people on the road in all parts of the world, and I know most are too sensible to go without health insurance, so could any of these people clue me in as to what is the standard process, is it done by country to country or one standard contract covering many countries?
Any and all tips would be much appreciated, cheers!