Mark:
Very fun topic. Three choices from UK courses I've played.
-- Boat of Garten's 15th. A 307 yard par 4, no bunkers, with a very deep depression about 200 yards from the tee. I've written on a previous thread that it can played (by an average golfer) as something of a 7 iron-7 iron hole. Or you drive into the depression -- it's only 11o yards to the middle of the green -- but it's totally blind and steeply uphill. Or you can try to drive over the depression, but it's at least a 220-230-yard carry. The green is very shallow, only 24 yards deep, forcing even more thought into the choice off the tee. Not the Boat's best hole, but its most electic.
-- Crail Balcomie's 7th, a 347 yard par 4. Somewhat similar to the opening hole at Prestwick -- a rock wall is OB right for two-thirds of the hole, and it is right next to the fairway. There is a huge falloff along the entire left side of the fairway, and the green -- bunkered right and back-left -- sits near the bottom of the depression. To catch the falloff and boost your ball forward requires a drive of about 270 yards. A fun hole, because the tee shot is so unnerving, as the wall/OB, deep falloff, and no sight of the green leaves one uncertain about the tee ball's prospects.
-- Machrihanish's 6th -- one of the many great par 4s on Mach's front nine, it's the quirkiest, with huge mounds, deep depressions, a solitary pit bunker, and fairway that's about as non-linear as it gets awaiting the golfer on the tee. A straight hole of 315 yards that looks anything but straight from the tee. The green sits in a bit of a hollow with two pit bunkers flanking left and right front.