T.W.
First--Congratulations!
There are a lot of great affordable restaurants around Portland--my two favorites are Cassidy's on 12th & Washington downtown, and Fernando's Hideaway (tapas), which is also downtown, though i can't remember exactly where. both have fantastic atmosphere. If healthy portions are a must, then i'd go with cassidy's--good, solid comfort food.
But what I'd really recommend is to go to portland.citysearch.com. they have a ton of restaurant reviews and even have lists of things like "top romantic restaurant"...I always look there when i want to try somewhere new.