What publicly accessible vantage points exist in Portland, Oregon?

I recommend the Pittock Mansion for a stunning view over Portland.

Depending on the kind of views you want, you might find that Washington Park offers what you need. It's set on hills just above the city, but with good public transport links to get there (MAX and Bus).

You need to be over on the Rose Garden side of the park to see the city. If it isn't the view you wanted, it's not the end of the world, as you're in the lovely Rose Garden at the time!

(You'll need the Rose Garden, rather than the Japanese Garden, as the latter has lots of trees on the entrance side which faces the city, with post of the gardens sunken down. Lovely, but not right for seeing the city)