Porto has some of the finest restaurants in Portugal.
Tŕ-se Bem: As one of the last restaurants along the river in the Gaia area,it was a great place to stop and have a lengthy lunch before heading out to do some port tasting. With delicious and hearty selections for a good price, it is also very popular with the local crowd during lunch it was completely full of people who work in the area. Skip the touristy cafes and head here for a authentic experience.
Casa Da Foz: Excellent Italian restaurant. Wide variety of dishes. Extremely small, so it's best to call ahead and reserve a table.
Varanda Da Barra: Great restaurant that serves traditional Portuguese, Italian and "International" food. Nice riverside view.
O Gaveto: Located in Matosinhos (norther part of greater Porto), it's one of the best (and at the same time, expensive) restaurants in the city, and in the whole of Portugal as well. Fresh, authentic Portuguese seafood restaurant. Expect to pay around €30-€40 per person. But it's worth it.