John,
I really don't know what "must play" means, but have to think the list is longer than just Sand Hills. Indeed, I'm thinking "must play" would mean a sampling of post 1960's courses that would give you a sense of what prominent architects have been doing and what different styles came into favor.
For example, its hard to imagine not including a course or two by Pete Dye, maybe PGA WEST, the Ocean Course or even Blackwolf Run. Then, too, you would want to see a totally man-made site like Tom Fazio's Shadow Creek. Conversely, I'd recommend the "8th Wonder" sites like The Old Head in Ireland or Cape Kidnappers in New Zealand.
In terms of "natural sites with good land for golf", I'd add Barnbougle Dunes along with Pacific Dunes. For affordable golf, you would have to sample places like Wild Horse or Rustic Canyon.
Finally, I'd recommend picking several courses of the architect or architects that you find most appealing. For example, if you favor Crenshaw and Coore, by all means go see Friars Head, in addition to Sand Hills.