Here are a couple which I forgot about in a previous post (I'm sorry, I do not recall the details of any of these three.

):
Here's a custom install of an aftermarket for a Mustang or something...
I've always thought that the wing from the 80's Corvettes might look good on the MKIII.
EDIT: I think the top three may be Do-Luck and Greddy... not 100% though.