I've done much of the trans-Siberian, and it's a great experience.

I'm wondering what other trans-continental train trips still exist. This would have to span the width (or length) of a continent. I'm assuming it's possible to cross the US by switching lines and zig-zigging, but is it possible to head along the same line continuously from coast to coast?

I believe there's an Australian one as well. Not sure that any exist for South America or Africa though?