I recently went through the process of picking a bike for a trip to South America that might extend to a RTW trip. I looked at many of the usual bikes and read a lot on Advrider and Horizons Unlimited. I ended up opting for the WR250R. It is light, very reliable, easy to work on, and has enough power for the trip.
At first it might seem on the small side, but consider the fact that in most of the places you will travel, people get around on little scooters or 125 and a 250 is a big bike with more than enough power. It can also cruise at highway speeds if need be.
This is probably not an option if you are going two-up.