What year car?
You can do an exhaust system upgrade... including a free-flow cat.
There's also a timing bump to 14 degrees. Won't work on cars with VVT (Variable Valve Timing)
There was an article somewhere (maybe linked off the pointy board) that detailed what some folks did on a normally aspirated car to increase performance. They used a different ECU, upgraded fuel pump & injectors, and some other things on the car.
You can also take out everything that isn't bolted down (and a lot of things that are!) to lighten the car. This will help improve the performance according to the butt dyno
RJ