TSAIS pro has a nice sound to it, also check out the CVEC and my current favorite is the OS T-2050. TSAIS is more high end, CVEC is adjustable for low-high and the OS is a midrange pipe.
Also look into THS, I haven't used them personally but I hear they perform better than stock.
You can also gear down to get increased acceleration. 3 speed mod would also be a good performance increase. I also like the werks clutch for better launches off the line.