The willow at Spring Valley's 6th (in fact, I can't think of a single willow tree I've encountered on a golf course that doesn't meet this criteria) should go. I was hoping the first day of the recent L/M tour, with its winds gusting up to 30 mph, might have helped further the good work done by an earlier storm, but to no avail.
I've always liked the "look" of the big tree on 13 at Lawsonia, because it's a solitary obstacle on a portion of the course (most of the back nine) that has virtually no internal trees. I was on the fairway left of the tree (a first!...that is, left of the tree from the golfer's perspective on the tee) during the recent outing. Interesing angle into the green.
I've never liked the tree there on 15, not just because as Dick says it blocks the bunker, but it also sort of dictates strategy for the golfer who might be tempted to fly the bunker, and create a shorter shot into the green, but is not long enough to carry the tree as well. Instead, the golfer who thinks flying the bunker might be worth the risk is dissuaded by the knowledge that he probably can't carry the tree. Langord's design strategy was all about creating rewards for taking the risky line off the tee, and the tree somewhat negates that for a decent number of golfers.