what do YOU mean by performance? forced induction, engine internals, or bolt ons?
forced induction, you can look to GM and get a supercharger, or you can piece together your own turbocharger setup.
engine internals, you can look in alot of different places. one website you can check out is
http://www.mantapart.com
bolt ons, you can look at a catback ehaust and muffler, or piecing together your own w/ a high flow cat, resonator, catback exhaust, and muffler.
hope this helps!