For the past few years, we've seen a recurring assignment involving this story from MSNBC, "Lost Cities of the Amazon Revealed," that has confused a number of students. It just came up again in chat reference, so I thought I'd mention here that students often ask for scholarly articles that cite this article. After some probing, it turns out that what they are really after are journal articles that talk about the discoveries that are mentioned in the MSNBC piece. If you plug in the name of the archaelogist, Heckenberger, and Brazil into any number of databases, you should be able to turn up good sources (Academic Search Premier worked well for this).
The 2003 article by Heckenberger et al about the discoveries can be found in Science.