In no particular order;
Diamond X, Billings, MT: this isn't so much a course as it is an experience. There is nothing quite like throwing up down around over under and off of literal 100 foot cliffs for 36 holes. There is nothing like The X anywhere that I have ever been.
Horning's Hideout, North Plains, OR: Only the Meadow Ridge course is needed for me to put Horning's on the list, but what really puts it over the top is the fact that there are 3 vastly different courses all in the same place. Meadow Ridge is a bit of a torture chamber, but in the best way possible while Canyon might be good enough to make the list on it's own. Also, I rarely have as much fun as when I am playing the Highland course. Short and easy, but it has all of the variety that you could ask for.
Milo McIver, Estacada, OR: In particular the Beaver State Fling layout is absolutely spectacular. There are so many unique challenges in the 36 holes. Also, this course is one of the fairest that I have ever played. An errant drive will punish you, but not cost you multiple strokes. There are very few holes that are "throw it near that tree and hope for the best." Additionally, it is extremely well-maintained and every hole feels like a new challenge.
Priest Pass, Helena, MT: This is a seasonal course that only has baskets during the Continental Classic Tournament every year, but when they are in it is among the best courses anywhere. Literally on top of the Continental Divide, you are playing at 5000'+ elevation. There is an amazing variety of shots required and no hole feels like any other. When the wind is blowing, the course will play 8 shots harder, but that just adds to the fun.
I know that this is supposed to be 5-10 long, but these are the ones that really stand out to me as better than anywhere else I have played. The next tier is
Adair Park, Adair OR
Blue Mountain, Missoula, MT
SeaTac, Seattle, WA
Pier Park, Portland, OR
Whistler's Bend, Roseburg, OR
Hickory Hills, Traverse City, MI