A few days ago, Patricia Ribeiro (About.com's Guide to Brazil Travel) started a conversation in the Peru forum about the Interoceanic Highway. If you don't already know, the Interoceanic is a new transcontinental highway connecting Brazil with Peru.
I'm eager to make the journey along this new route, but it will have to wait until next year. In the meantime, I'd love to hear from you if you've already been along any sections of the highway.
Another Peru to Brazil option, of course, is the Amazon River and its tributaries. From Yurimaguas, just a few hours from my base in Tarapoto, I can hop on a boat to Iquitos and then keep going all the way to Belém on the coast of Brazil. That would be an epic voyage, and one that I hope to make at some point.
If you'd like to join in with the discussion, head over to the Brazil-Peru Travel thread in my Peru travel forum.