I know you are going to Peru to see Machu Picchu, as well you should, but just remember that the Incas were not the only people in pre-colonial Peru. The Nazca people pre-date the Incas by a thousand or more years.
A must-see are the Nazca lines. Flying over in a steeply banking light plane is not for the faint of heart, but if you like flying, it is an amazing experience. There are as many theories and to what the lines and geoglyphs represent and who or why they were made, there are figures in the sand (some 300 geometric figures and 300 straight lines over 500 sq km of desert) and comparing stories from various guides is half the fun.
Another extremely popular tour from Nazca is the Chauchilla Cemetery. Dated from approximately AD1000, the cemetery has been restored from the remains left by grave robbers to provide a look into the burial rites of this ancient people. Certainly an afternoon well spent for anyone who enjoys learning about ancient culture and/or looking at ancient mummies and bones.
If time permits, look for a colectivo taxi from Nazca through Ica to Huacachina, a little over 2 hours away. This beautiful oasis surrounded by towering sand dunes is a great place to chill out over lunch and maybe try your hand at sandboarding.