According to this report out today from Peru's government newswire Andina, the source of the Amazon has finally been officialy nailed down to the Apacheta Quebrada, in the Caylloma region of Peru. The high resolution satellite image work done by The Geographical Society of Lima ratifies the findings of the 1996 'Amazon Source' expedition, with the Apacheta source winning out over the only other candidate by 691 metres.
And yes, before you ask The Amazon's near 7000km length beats out The Nile's 6,671km.