We love Portugal. There is an authentic friendliness from the people that is special.
Lisbon is great for three days, more if you do day trips to Sintra and Evora.
Then head toward Porto. Perhaps renting a car to go from Lisbon to Porto.
Stop off in Cascais, Obidos, Batila Cathedral and Navarre.
Spend about three nights in Porto with a day trip to Santiago de Compostela in Galacia, Spain.
Consider taking a cruise up the Douro River. We did a fantastic seven day cruise. You can do a day cruise if you like. Take the train up the river valley or rent a car.
Here is my review of our trip.
Portugal, the Douro River and a bit of Spain
http://www.cruisecritic.com/memberreviews/memberreview.cfm?EntryID=535267