well - if you want to tune an es- i guees you would need a custom exhaust setup, as I believe there aren't any bolt on ones. there are for the IS and GS but not too sure about the ES. You can start by getting a K&N air filter, custom exhaust (borla?freeflow...) Platinum plugs,performance wires,um...strut tower brace, lowering springs /shocks/struts. you might as well go the handling route too.
but honestly, one is better off doing this much work and spending this much money on a sports sedan. we own rolling sofas, and by no means are they intended to be "hopped up". I understand we all need to make statements or try to be different, but this is just the wrong car for them IMHO.
the money you save one can get a sports car if you want! fast right out the gate!