I didn't like Porto (I am apparently in the minority, but you asked). However, I did like the Serralves Museum (including its park) and the Soares dos Reis National Museum (great sculptures by its namesake - very Bernini-like - as well as paintings by Portuguese artists I hadn't heard of or seen elsewhere).
In Lisbon, tourists I met there insisted I go to the Pavilhão Chinês, and I'm glad they did. It's a "bar," but I just had tea. Each room is decorated with collections of old toys - very atmospheric.
I didn't get to the Gulbenkian Museum in Lisbon, but friends who did said it was their absolute highlight - next time!
I spent overnights in Santarem, but it can also be seen as a day trip from Lisbon. It's at a very scenic bend in the river, and has several lovely churches. The Igreja da Graça with its rose window is more famous, but I found the azulejos (tiles) in the Igreja de Marvila even more beautiful and amazing.