For anyone planning global travel, Kevin Kelly (of Whole Earth and Wired fame) recommends the book The Practical Nomad: Long-term global travel:
Round-the-world travel was my occupation for many years. It's an admirable vocation ignored by the travel industry and travel media. They think in terms of two weeks not two months or two years. Ignore the country-specific info in this thick tome as out of date, but do pay attention to his airline ticketing advice, and his general wisdom about long-term travel.
"But if you want the cheapest possible roundtrip from the US to India, Ireland, Nigeria, or any other place from which there are large numbers of immigrants, no general-purpose agency, even a general discount agency, is likely to be able to beat the lowest prices of a no-service, bare-bones, specialist agency within that particular ethnic community that sells nothing else but a massive volume of roundtrip tickets to a single destination."
While you're at it, you might want to browse the rest of Kevin's fun "cool tools" page. The tools he chooses sometimes veer off into the expensive toy or just-plain-odd categories, but it's still a worthwhile half-hour of tooling around.