It's surprising how many people go abroad without taking out insurance. Even if they do, it can often be inadequate or not suitable. It's not worth the risk! Here is some good advice about insurance from the FCO: www.fco.gov.uk
Here are some companies which specialise in gap year insurance:
'This is specialist travel insurance designed for people on round the world or multi-stop trips. The 24/7 medical emergency hot-line is staffed by people who are experienced in dealing with incidents in all parts of the world.'
Some others include: