Oregon - quite possibly my favorite state for landscape photography.
Like others have said, spend some time with the Columbia River Gorge and work the waterfalls and the general beauty of the area, and of course head down and hit Crater Lake. If you have an interesting light day, the lighthouses at Newport (Yaquina head) and Florence area (Heceta head) along the coast are quite nice too. Take some of the roads from the coast to the inland through the wine country, or further south near the Rogue river. This state is absolutely gorgeous, and might have the greatest mix of different types of landscape scenery of them all.
I will play contrarian to one of the other posters and say I prefer Bandon (and to some degree, Gold Beach as well, perhaps an hour further south) for coastal area/seastacks to anything in the Olympic NP coast, and I also have done both a few times. I'd go farther and say that of everything I've photographed in my life, my top two favorite photographic experiences were 1) shooting Glacier National Park in the early 90's and 2) discovering Bandon Beach and having an absolute blast shooting amongst the low tide seastacks at sunset. (#3 would be my first time in lower antelope slot near Page, AZ, but that's a different part of the US). There are some nice viewpoints from Cape Sebastion a touch south from Gold Beach too. Hell, I'm not sure I could criticize anything on the entire Oregon coast - one could spend a lifetime shooting it.
Don't skip Olympic NP and while I have a preference for the Oregon coastal area, hit the beaches here as others have said. Hit the ridge road to the peaks, and hit the rainforrest too. Forks is a nice base for this area, and I've had good luck at the Forks Motel.