Alright, I am adding a note about the banggai cardinal because you are both right. Though they are not impossible to keep, buyer should be aware that they can be quite finicky and do not ship well. That also reminded me to add a note about the neon goby, so, thanks! Both of those have been added, as well as the remora shark and pinecone fish.
Melly, I do not want too much debate on this list. I want this to be a pretty straight forward list. For that reason, I don't think baby hippos need to be on there, per say. I have worked at two reputable LFS in my time in this hobby. The one I worked at could not ever keep baby hippos alive. They would come in, and never eat. The second LFS I worked at had incredible success with baby hippo tangs, with most eating and growing very well. I think it all depends on which shipper you get the hippos from. There are some that collect and ship them great, and there are some that ship them terribly.
Katz, I will compile a butterfly list next listing all of the common species, and the ones that do well and the ones that should be avoided.
Gina, you asking me about the spiny oyster has actually prompted me to add that to the list. Thus, info on that guy is now above!
I would like to thank everyone for the comments/questions so far, keep them coming!