Well, Machu Pichu in Peru is a don't miss. then take the train from Cuzco to Puno (on lake Titicaca on the Bolivian border - floating village there). Then go to Arequipa (beautiful city, wish I could live there), then Ica (the Nazca lines), then back up to Lima.
Get as high in the Andes as you can stand, but watch for altitude sickness (seroche?). The meadows and mountains, Llamas, villages are beautiful, and the light amazing. Go out in the small villages at night, listen to the traditional music and watch the dancing. Eat the food, don't ask what it is. Don't drink too much of the local moonshine.
How much time do you have? Whatever it is, it's not enough! If you have more time & $, go to Iquitos on the Amazon, and/or Pucallpa. Take a trip on the river, watch out for crocs and snakes (oh I almost forgot, Australia has most of the poisonous ones anyway)!
Try and learn a few words of Spanish before you go. Baņo and cerveza are the two most important.
Wherever you decide to go, you will love it.