Depends on how you are getting there, to be honest. I would recommend Easter Island, but very expensive to go to if you are buying a ticket outright. Cuzco and Macchu Picchu are way up there on my "did it" list, and both are amazing. In my opinion, anyway. I seem to remember someone being thoroughly underwhelmed when they compared MP to the Pyramids in Egypt. I have not been to Buenos Aires, but have been told it is a cool place to go. Want to go and learn the tango one of these years.

If you are on a RTW, consider Easter Island and Lima, and get a side ticket to Cuzco. Depending on how much time you have, take the trip through Arequipa, Lake Titicaca, and down to La Paz. Easter Island hotels will run from $30 to $130 a night, but the accomodations are still rather spartan regardless of where you stay. Anywhere in the Andean highlands, you can go for a few bucks or a wad of cash. I dont remember the names off hand, but I stayed in a guest house for 10 soles when I was there, down the street from a hotel that was built in a monestary that charged about $200, iirc. Poked my head in, and it looked *very* nice.

I didn't include Brazil because I don't really know much about it other than they bent me over on a visa technicality, and I refuse to pay another $65 for something so silly. Needless to say, I haven't been there.

If you take Lan Chile, you will have to connect through Santiago. Worth a couple of days, because it's a really nice city, but any more and it gets boring unless you go outside the city to Vina del Mar or somewhere. But it is not the most exciting of places, it's just a nice place to be. Can't help on the rest of Chile, but I would like to eventually go see the penguins in the south.