So, as is common in the movie industry, WETA considered a variety of different designs for Smaug before settling on what we got to see in The Hobbit movies. And designer Andrew Baker has posted a big batch of those designs on his blog under the heading Smaug Fails.
Looking at what he has posted, I think it's safe to say that he's being self-deprecating on this one. Not all of the designs would have fit the style of the movie certainly. And some wouldn't have captured the right feel for Smaug. But they are all visually arresting in their own right.
Make sure to click through and check out the entire collection.