· Go North-South, versus East-West:
For obvious reasons (like the existence of oceans), you won't be able to do a pure lateral journey on buses. Instead, why not go longitudinal as Andrew Evans did for Bus2Antarctica? We say pick two north-south routes like Calgary to Ushuaia and Sapporo to Wellington. That way, you can do one before the other and not take off as much time from work. Obviously the Sapporo to Wellington route will involve some ferries, but it'll also have you on some of Japan's very nice buses, maybe some in South Korea, and then we suggest hopping over to China for some of their double-decker sleeper routes. See the list of resource sites below for more information.
· Pick several countries and take buses all around them:
Conquer around-the-world country by country, and the easiest way to begin doing this is by touring your own country for a start. Greyhound offers a Discovery Pass that allows you unlimited stopovers and mileage in the US and Canada for your choice of days, with a 7-day starting at only $199. Keep a map at home and color in each country as you finish taking buses throughout it. You can easily make a belt around the world over several vacation periods. A few country suggestions where this would be great: the US, Mexico, all of Europe, the Ukraine, Mongolia, China, Japan, Australia, and New Zealand.
Just remember to use common sense and stay safe when you ride the bus. No bus rides through Pakistan or East Timor, okay?