Well I am going to use part of my tax refund to do some mods. The only thing that I have done to my car is add 20's, tint and clear corners. What are some performance additions that would increase my performance.

I would suggest a Z tube and a MortorDyne plenum spacer for starters.

MREV
Intake

^^^
he cant get MREV, he's got an auto 03, mrev is only for 05-06 6mt.
I'd do what andy suggested plus maybe a popcharger or panel filter.
some underdrive pulley's would be a nice addition if you dont have a sound system.
-GP-

If you are going for looks, maybe a front lip if you don't have one, mrev, intake.

for $1500 you can get the Ztube, Popcharger or just K&N, Plenum Spacer, High flow cats, Generic Ypipe, and a moderately priced exhaust. That's only if you save money on the install and put them on yourself and you shop around. That's around how much my setup ended up costing.

plenum, high flow cats, and intake

Z-tube, popcharger, MD spacer, Gord's grounding gear, and fujitsubo y-pipe.
add some $$ to get Fujitsubo exhaust..get that all install by yourself..

invest?

^^ +1 keep it in the bank.

You're in better shape than the guy with only $300 for mods in here.

same as everyone else's suggestion... intake, spacer, exhaust (cats if you can get those in under your budget). Heard a lot about grounding wires for the 5AT, more positive reviews than for the 6mt, so try that for a cheap item.

$1500...

intake (pop-charger, Z-tube, ISO plenum spacer), sway bars, clear bra.