Portland has some great restaurants and the scene here is casual; rarely do you need to dress up for anything.
East side near-ish where you are staying:
Ken's Artisan Pizza (SE Pine St & 28th). I love this place! You can grab a drink if there's a line or eat at the small bar, right across from the wood-burning oven. Great date place.
Apizza Scholls (SE Hawthorne & 48th): very similar to above. Either is a great place.
?Porque No? is a casual (and open-late) taqueria (Hawthorne & 47th): http://www.porquenotacos.com/
Definitely head to Departures, a new bar on the top floor of the Nines Hotel downtown. This used to be a department store, but had been redone as a high-end hotel. The views on the outside bar areas are some of the best in town: http://departureportland.com/, go to "gallery" and check out the photos!
Edit: Bluehour in the Pearl District for drinks. It's right next door to Wieden+Kennedy, the big ad agency who moved into the Pearl when it was still mostly warehouses and really prompted that area's transition.
For a really nice meal (maybe dress up a bit!), try Higgins downtown. One of the first and best places emphasizing local cuisine.
+1 for Bridgeport Brewery (the one in the Pearl at NW 14th + Marshall).
Edit: my recommendations are for in the city (except for the Gorge and especially Multnomah Falls). I'm assuming you won't necessarily have time with a wedding weekend to travel to the coast. If you do, then a big +1 for the coast, especially Ecola State Park & Cannon Beach, and Astoria.