Leesee here:
things you really should try if you haven't before:

Chicharonnes (tasty, tasty pigs)
Anticuchos (OMFG good)
Papas a la Huancaina (a common working class dish)
Ceviche and Pisco Sours are well known, sounds like you've had them already?
Causa - especially if it is noted as a 'Causa Limena'
Lomo Saltado (a mid-coastal creole dish)
as many empanadas as you can throw down
Rocoto - for christmas some peruvian friends sent me a jar of these peppers... I'm pretty much forever in their debt. It should be noted, the Schofield rating is 50K-250K. (comparison: Jalepenos are 2500 to 10K) the hot ones will blister the skin on your hands if you pick them up without gloves... that said, the taste is smokey and has body... and it only takes a drop or two in a whole bowl of soup.


Dessert:
Picarrones - I still dream about these, they are frequently found in food carts on street corners - they smell sorta like a pumpkin doughnut would, but the taste is different. You want them.
Manjar Blanco - the article is a good explaination, but my favorite way to eat it is in crusty pasty horns, filled with the stuff. It is completely, completely incredible.
Turron - is an experience, but is often only available seasonally. A small piece goes a long way.
Suspero a la Limena - fantastic stuff, but primarily only found in high-end restaurants


Run like hell from:
Carapulcra (wikipedia says it is appetizing, it is one of three or so foods tha make me want to vomit)
Chuno - freeze dried in ice rivers, trampled by habitually barefoot peasants, left in the sun to dehydrate, and most unfortunately, a delicacy & social honor of the highest order... if someone serves it to you in the andes, they paid a vast sum of money (for them) for it, and they almost couldn't give you a higher honor. Also unfortunately, it is one of the other things on my list of foods that make me want to vomit.


right - I didn't cover interior-andes food, assuming that you probably won't run into much of it. If I'm wrong, let me know, the food there tends to be quite distinct from the food on the coast.