John Day Fossil Beds off 395. I think that is the most beautiful country, and the town of John Day has an awesome Chinese Museum that is a must see.
Joseph - its out of the way, but beautiful country and a neat little town
Crater Lake - You can't go to Oregon without visiting the most beautiful lake in the world.
I second McMinnville Air Museum, in fact, it was the first thing that came to mind when I thought of places in Oregon.
If your a history buff, the Lewis and Clark Fort Clatsop is interesting.
An Ice Cream cone at Tillamook Cheese Factory
The whole coast, north to south.
Happy Travels