http://imgur.com/a/ysuwy#avBYFI was moving around, and found the Terrain Generator made floating bits. (Light picture) Then I moved on and found an awesome gorge into this plateau or whatever, and skeletons/spiders/Creepers kept spawning out of it until I filled it with torches. (Darker picture, second one showing Skeleton that came out of it)
The rest of them... I found a group of like 7-8 Enderman on top of this mountain type thing. I moved around and discovered it was actually 10-11. However, I couldn't group them too well since Creepers kept coming between us. Weirder still, even with like 7-8 Enderman actively following me, I'd see more out on nearby mountains. My last few show 10 following me at once.
Edit: One of the images in the above link.