More track time. Becoming a better rider has been, by far, the greatest mod I could have ever done. Another nice thing about it is that it works on all bikes, no matter if on the street or on the track.
Second to that was actually getting a second bike, strictly for track use. A little bit of "its ok if I crash this one, not ok to crash my brand new CBR" gave me a lot more confidence and really allowed me to push a little harder which is one of teh things that allowed me to become a better rider.
Old thread, but
Other than that, Suspension/Geometry adjustments, SS brake lines, Brembo MC and SBS Dual Carbon Pads, 520 kit with different gearing and good tires.