For performance, here's some idea's:
Intake- decent power (7-9 horsies), pretty nice sounding noise.-
www.frankencar.com, www.custommaxima.com, www.injen.com
Exhaust- 12-17 horsies, nice sound. Don't go cheap.-
www.greddy.com, www.stillen.com
Y-pipe- best mod available besides big $$$ projects, 20 horsies, minimal exhaust sound, nice gains.-
www.budgetexhaust.com, www.stillen.com, www.warpspeedperformance.com
underdrive pulley(UDP)- lightens up stock pulley, no noise, 7-9 horsies.-
www.custommaxima.com
All are pretty inexpensive.