John:
I think the greatest par-3 I ever saw without a bunker was the old 7th at Royal Liverpool, known as the Dowie. It was 200 yards, with a shallow swale at the front right of the green, and o.b. hard against the left side of the green ... like, 5 feet off the putting surface. Just an amazing hole to watch people "attack".
The Dell Hole at Lahinch is another top pick.
Also, I can't remember for sure, but I think the 5th at Royal Worlington & Newmarket, the great nine-hole course near Cambridge, is bunkerless. There is a stream that you could wind up in to the right, and a deep grassy hollow to the left, with a three-tiered green on a ridge in between that someone once likened to a vaulting horse. I should build a hole like THAT somewhere, even though it would probably be the last course I ever built.