Most people here have too good of taste to recommend what you want here... But the inner ricer in me (and it grows strong) likes what this guy did with an eBay spoiler:
In another video he says it shakes scarily above 70mph so get ready to enjoy a lack of safety for you and those driving in your vicinity. If it doesn't fly off catastrophically, though, you can expect reduced highway fuel efficiency and a greatly reduced top speed....
But I do think it looks cool sitting still. In this particular case, I have shamed my inner ricer into minding it's own business. It would probably be prudent for you to do the same.
.....It looks cool though.