Agreed that the crowds can make some of these classic hikes not necessarily the best hikes. It's the classic hikes that I was wondering about with this question, so I just updated the thread title to reflect that.
One that falls in this category that's not on the list and that I've been looking into is the Tour du Mont Blanc.
EDIT: Actually, scratch that. I guess what I'm interested in is the best hikes in the world in terms of scenery or just being unique in some way, regardless of whether they are a crowded classic or the super secret hike that nobody else knows about....although I assume that latter will not be revealed here.