Dr. Benway
Google
Just went here for my birthday. It was quite expensive, but you're paying for quality here. The food is made with fresh, locally sourced ingredients, and the tastes go well together. I liked the way a lot of the dishes seemed really creative (I'd have never thought to include pickled cherries but they sure were tasty!). The drinks there are great too, not too sweet. I also appreciated the subdued but not stiflingly fancy atmosphere. Obviously, you'll want to make reservations if you're working on a specific timetable or have a larger party.
On a side note, the location is nice and has good parking, is readily accessible by public transit, and less than 10 minutes away from a lot of interesting shops over in the Northwest district; this is useful if you want to make a full day of your visit to Portland.
Summary: All the buzz I'd heard was right, and it's great for any celebrations, just be prepared to either spend a lot or split the bill.