if you like pizza with deliciously buttery crust, try Old Town Pizza. They have two locations. Go to the one on the east side of the river if you want a good pizza in a cool retro/reclaimed wood themed place. Go to the one on the west side if you want to see a bathroom decorated by the serial killer from the movie Seven.
If you have time, a car, and like to hike, Angels Rest is a pretty cool place to go. It's in the gorge. Whatever you do, don't waste your time going to the tourist trap that is Multnomah Falls. It's pretty cool to look at from the bottom where the bridge is, but the hike is boring and the 'summit' is lame, even after they built the 'viewing platform'. Stop there for 20 mins, check it out from the bridge, then continue on down 84 to Angels Rest.