Got a few additions to the list...
Mace's Rainbow Inn, Cathlamet, Washington
Awesome burgers, great fries and no line. Its kinda out of the way unless you're driving the slow way to Astoria. Or you can take the ferry across from Westport, Oregon. This is one of those classic small town burger joints that somehow have burgers that make you smile with every bite. The sun faded menu has obviously shrunken over the years but they still have the same great selection of milkshakes. I recommend the curly fries.
Pheasant Grill Drive In, Arlington, Oregon
First off, the location on the map is incorrect, the restaurant is actually at the intersection of Locust and W 1st in Arlington. I haven't been here since the new owners took over but I hear they've only improved things. Instead of a bag of lays with your local beef hamburger, you get fresh "homemade" potato chips. The potato salad is to die for and because the owners are Samoan, they have delicious macaroni salad.
Fields Station, Fields, Oregon
An all-purpose business, it is the only year-round gas station/motel/grocery/liquor store for 100+ miles. Where else can you pay for a burger, a night in the hotel and a bottle of Jack (sorry, they have a limited selection) with one swipe of the credit card? Oh yeah, the burgers, best of the bunch. Sandy, the owner, can usually tell you which local farm the beef came from. Her husband, Tom, is very knowledgeable about the area and can tell you the condition of any road. Back to the food. The kitchen is in the middle of the 15-seat restaurant so you can watch Sandy cook your meal. Also fantastic for breakfast and their shakes are world famous. (don't believe me? Look at the guest book, last time I was there I signed after a guy from Scotland) It is a long way from anywhere but it is worth the trip and the scenery in the area is spectacular.
The restaurant/store/motel office
Sandy, the owner, making lunch.
The yearly tally of burgers and shakes sold.
A bacon cheeseburger w/fries.
Liquor store and candy aisle.
A good place to camp 20 minutes up the road.
The view across the road in the winter (got down to 8 degrees that night)