I recently discovered this nice Peruvian restaurant in Los Jardines, called Machu Picchu - on Dr. Arturo Grullon between Texas and Metropolitana. Great ceviche as well as other dishes, moderately priced.
I like Marisco Cibae?o, previously known as Marisco Centro, near Av. Francia in the Monument area. The Quiosco outside are a nice place to eat then pass the time talking while having some drinks with friends.
if your in santiago you need to stop in to hooters in the terramall, just for the sites and cold beer, and yes they also have food i believe.if you go say hello to yasmin for me.