I remember playing golf with a friend of mine several years ago who asked if I had played a particular course. I hadn't. He replied, "Your golf education is not complete until you have played it."
I have kept that thought in my head for a long time. There are some courses that eveyone needs to play to be able to understand golf course architecture more completely.
Just for starters I'd list the following courses in GB&I:
Prestwick, The Old Course, North Berwick, Royal North Devon, Royal Dornoch, Royal County Down, Ballybunion, Sunningdale, and Walton Heath.