A tip for you since you're fairly new to the forum
@Van Beal: if you want to get an idea of whether a species is rare or not, you can use the search bar to search the forum for references to that species. You can also do this in the media gallery to see where photos of these animals have been posted from. Doing so will be able to rule out many of these species for you. As you can probably guess, the bar is pretty high for "zoo animal that few zoo enthusiasts have seen"
I'm working on a resource that hopefully will give everyone a decent idea of what herps are common or rare in the United States, but for now I can confidently say that the skink (also called Prehensile-tailed Skink) is one of the most common lizard species found in zoos.