In Porto: Almost impossible to find real portuguese food in the city center. However, Palmeira, at Rua Sá da Bandeira, is still the real thing.
But, not that far, you have:
- Verde Minho: cheap and very good, Try to have dinner there once. (Rua de Camões 725). Very good meat (Posta à Mirandesa. a special dish from northereast Portugal, is really good). Closest metro station is Faria Guimarães, yellow line towards Hospital de São João.
- For "francesinha" (search google if you don't know what it is) you have "Rio de Janeiro", at Carvalhido (Bus 508, and others, take you there). Go early and visit the nearby "Casa da Prelada" with it's big labyrinth (the biggest in Iberia). And the church, it's nice.
A litle bit more outside: Tia Aninhas, I don't have the slightest idea how to get there, sorry. Also unexpensive.
For fresh fish and seafood, you should go to Matosinhos (Metro, bus 500, bus 501) at Rua Heróis de França. Or to Afurada (on the other side of the river, a kind of taxi boat can be taken at bus stop "gas". Bus 500).
And that's all I can remember know.