I'll limit my suggestions to the Old Port area assuming that someone here for only one night might want to stay in that part of town.
Hugo's for their tasting with wine pairings (also your most expensive option)
Fore Street - consistently great though not as adventurous as some others. They invented farm to table.
Miyake for the omakase. Creative sushi (plus cooked non-fish items often fresh from Masa Miyake's farm). Half the price of what you would pay in a big city. Sake pairings available.
Bresca - very, very small. Best deserts in town.
Street and Company - in past couple of years the reviews have been a bit mixed (I'm a fan). The best pure seafood play in town.
There are many more great restaurants in the Old Port (the main tourist area though at this time of year, on a Tuesday, it will be a local crowd) but these seem to make most "best of" lists.
hi! I'm going to jump in here b/c I'm looking for similar information. My husband and I are coming to Portland for a couple days this summer. I'm from the Boston area (he's from Kentucky) and we LOVE to eat. We like places with local food [both local literally and local like "traditional of the area"] and good atmosphere. We prefer small places, too! I'm going to check out the places you mentioned above, but I was wondering if there's anything outside the city that any of you feel is a must-go. We're ok spending a decent amount. And we're psyched about a hole in the wall/out of the way kind of place. Thanks so much!