I've been researching into airfares and it seems that the best option for me will be a round the world ticket. I've been looking into two types of ticket, the Star Alliance RTW ticket and the One World RTW ticket.
Both alliances have mileage calculators.
I found that in general Star Alliance airlines were quite difficult to deal with, their call centres didn't seem to have much knowledge of or be geared up to deal with this kind of product, after calling BMI and Air Canada, I eventually called Lufthansa and got pretty good help.
One World were a lot better, I spoke to a sales person at BA and from then on she kept me up to date and helped my tailor my ticket, I also had direct access to her, which meant I didn't have to start from the beginning each time I called.
Both tickets require you to travel in the same direction all the time, i.e. east or west and you can only cross the pacific and the atlantic once. The key difference for me is that Star Alliance required every flight to continue in the same direction (apart from connections), whereas One World only requires that the continents are travelled through in the same direction, so for example in Asia Pacific, I can travel any direction I want.
Here are the details of each:
http://www.staralliance.com/en/travellers/tools_services/round_the_world_mileage_calculator.html
http://www.oneworld.com/ow/air-travel-options/round-the-world-fares/oneworld-explorer#example-itineraries
