l already have exhaust, tint, and a sound system.

Depends on what you're going for. If u have a sound system l am guessing you're going more for looks than speed. If that is the case, it is all about ur personal taste. If u want speed, u will need to decide how much u want to spend. An exhaust is a decent start as long as it is a FULL exhaust system & not just a muffler or a rear section exhaust. A full catback is what l will assume u have. Now u really need to plan what u want to do next.

If u plan on staying non-turbo or going with Nitrous eventually, I'd look into a simple set of headers & a Cold Air Intake system. From there u would most likely want to go with the Nitrous kit. If u decide on Nitrous, limit yourself to a 75hp shot, & make sure the kit has a bottle warmer, throttle position switch, & an window switch to make sure the nitrous does not turn on at too low an RPM. You will also need to swap ur spark plugs for ones that r 2 heat ranges colder.

For Nitrous, Turbo, or Supercharged applications, u will need to start using a MINIMUM of 91 octane & use ONLY synthetic oils like Royal Purple, Redline or Eneos every 3K miles. I'd also, make sure ur fuel system is ok & change the fuel filter regularly.

For a Turbo setup, there r a few kits that r mostly bolt on & include everything u will need. Supercharger kits r the same. l will leave u some links to help u out.
Intakes/Headers/Exhaust Systems:
http://andysautosport.com/scion/2005_9999_tc/performance/intakes/cold_air_intakes/
http://andysautosport.com/scion/2005_9999_tc/performance/headers/
http://andysautosport.com/scion/2005_9999_tc/performance/exhaust/cat_back_exhausts/

Nitrous Kits: I'd call for ur application
nitrousexpress.com
zexnitrous.com

Turbo Kits:
http://turbo-kits.com/tC_turbo_kits.html
http://greddy.com/products/display/?Category=turbo&SubCategory=15

Supercharger:
http://intensepower.com/trdsukittc.html

Hope this helps u out & gives u a few options!

change s2000 antenna, get some hids, paint rims (save cash for new shoes) Mine are gold , cold air intake, springs and shocks...