Accessories aren't cheap. The most improvement can be seen by:
1) Custom Superchips Tune from BamaChips or Troyer Performance
2) Catback Exhaust - Magnaflow is highly regarded as researching exhaust gas velocities and building their systems around that
3) a cold air intake kit
You're talking about 1000 bones for this, but it's the best bang for the buck if you're looking for upgrades.
There's numerous other mods you can do, look at each forums "sticky" section as a guide to these.