I've often thought that a motorcycle trip through Mexico, Central and South America would be a trip of a lifetime.
If I can ever get my hands on one of these I might give it a try:

Daylong makes a good comfortable saddle for it and it gets 100 mpg.
It has a 5 gallon tank and if you hang a 5 gallon jerry can off of each side you can go 1500 mi between gas stations.