Before I set off, there are so many options of different transport methods to travel around. In South America buses seem to be the only real way to get around easily but also seem to be great value for long distances. The advice I've received so far about this, is don't sit next to big fat men who chew coca leaves on buses with no heating.
For the US & Canada, the greyhound bus service do a 2 month unlimited Discovery Pass which allows you to travel all over the country. That looks like it will be the plan from the time I hit up SXSW in Austin. I'm using Skyscanner to look up flights from all the various airlines, a great tool to help find the cheapest flights on the dates you want from pretty much anywhere in the world.