Porto is heaven for your palate. You have the choice between fancy, trendy restaurants with modern cuisine or authentic, Portuguese mostly quite cheap. Here are my top picks for Porto:
O Buraco, Rua do Bolhão 95:
Portugese restaurant. Not fancy, but delicious food, especially the grilled fish. Low prices
Adega São Nicolau, R. de São Nicolau 1:
Portuguese Restaurant, not very cheap, but friendly service and good food
Traça, Largo São Domingos 88:
Trendy restaurant with a nice atmosphere and mediterranean food.
Terra, Rua do Padrão 103:
Excellent food - sushi and mediterranean - a bit pricy. Reservation in advance recommended.
Restaurante Augusto, Rua da Constituicao 1064:
Authentic Portuguese restaurant for great food for nothing.