Like splash said, you could go with a leopard, but it will outgrow your tank. IMO a gray smoothhound would be a better choice, as they do not grow as big, are active, and still fit the stereotypical shark look. But, they will outgrow you tank as well. You will need to secure a future home for the shark before you buy it. This can be a real problem unless you have connections. I.E. Someone who knows people with $$ and huge tanks. Public aquariums are not interested in the sharks commonly available in the hobby. They just get too many offers, and most of the time, their tanks are stocked, meaning there is no room.
Its been my experience that nurse sharks are a dime a dozen. I find this unfortunate, because nobody will take an overgrown nurse (especially public aquariums) and you may end up having to kill the shark.
Unless you find a guaranteed future home for the sharks, I think you'd be happier with something like a bamboo. IMO, adult bamboo's look like nurse sharks anyway.
