Oh gosh there are so, so many of these....and I think about them all the time and get giddy (even though its been years since I hit most of em).
1) Being able to see that I actually did indeed have collar bones! No one was sure for the first 25years.
2) Not seeing, but being able to find my hip bone. I distinctly remember laying on a x-ray table at 240lbs and the tech not being able to find my hip bone and therefore place the xray machine appropriately. He was disgusted, I was so ashamed.
3) Seeing my ribs...this one is recent. I can actually see all of them at all times now. My torso is super slim, legs carry most of my body fat now.
4) Physical stuff. Being able to do...anything. I couldnt walk a single flight of stairs comfortable. At first it was those small victories and now its getting better at the gym. Agility too - I was recently struck by a car as a pedestrian and jumped mostly out of the way (yay reflexes and muscle strength!) .