it depends on what you like. I can spent hours in Powell Books
Actually, their Rose garden is free and has a nice view of the city. I went close to sunset last time. But it's been like 4 years since I went there... and this is not really the rose season now..
if you plan to head outside of portland (oregon coast) there is the canon beach and the haystack rock. BUT it's getting cold and windy now....
For within portland, I like the Pearl District. It's like a family style yaletown there...
I would like to check out the Saturaday and Sunday Market but I missed it last time I went there.