Radar detector ! You will find yourself driving your car faster and harder when you have some protection against the cops.
All kidding aside, I would definitely invest in a really nice cold air intake, such as one from AEM or Dinan. It won't cost the full $500 (so you'll have some loot leftover for that radar detector
![Stick Out Tongue [:p] [:p]](/images/smilies/tongue.png)
), and you can install it yourself so you don't have to spend any more money on installation. It will also give the car a more aggressive tone under hard acceleration.