Here is a clip of the Instant-G exhuast upgrade. Other than a loud drone at around 2600 rpm (too low of any rpm for me anyhow), I really like this system.
I've also recently installed Bilstein PSS9 suspension along with Michelin Pilot Sport Cups. This is becoming a fun track/street car.
http://www.youtube.com/watch?v=ycKHhtPFxZ0