Definitely one of my favorite areas!
Viana de Costelo (big beach at Cabedelo, go to point B and head to beach:
http://goo.gl/maps/O8wes) has a great bay that usually offers nice waves (and can be super flat water in between the spread out waves)
Esposende (Ofir) has a really great flat water spot in the river (go to point B and walk in on the board walk to the spot on the dune on the riverside to setup/launch:
http://goo.gl/maps/4OIXZ)
I'm sure even right near Afife you can get good waves (pending the tide schedule) along the coast.
The big city beach (nice place) at Matosinhos (Oporto) is great with S winds and offers good waves too if you happen to be in Oporto. Local Porto kiters:
http://www.facebook.com/groups/163449700353308/
I'll be there for the month of June...I'm stoked.