jdoc

I have an Is350... with Tom's Supercharger... one and the only one in USA.

The question is "what" and "how much".
What do you want your car to be?
How much do you have in budget?

Sorry, but there is pretty much no way you can make your car faster because Toyota has full control of the car with their ECU.  Unless you want to put in another engine...

You can spend money on coilovers (or airbag suspension) if your road condition allows driving low.  Airbox and Intake system will not help to boost your car.  You can change the exhaust to make it sounds beefy.  You can get up to 19" of wheels if you don't mind stiff driving.

If you are planning to get wheels, spend at least $2,000US on wheels.  Because your original wheels cost more than $3,000US and very good quality built, and usually people getting wheels ending up down-grading the wheels because they are getting cheap wheels that has lower quality than your original wheels.

Good luck and have fun with your car.