What Modifications Should I Make To My '04 WRX Sedan?

I bought it new, and waited until the warranty was up to do much to it. The end of the warranty came and went, and I still have done very little to the car.

So far, I have taken out the ram air scoop and air intake silencer, and flashed the ECU with a Cobb AccessPort, which has since been stolen. (I changed the base map to performance mode for 93 octane before that sad, sad morning).

I don't intend to ever get rid of the car, and I don't currently use it as a daily driver. It's just been so close to stock for so long that it's time to make some modifications. I'd like to start cheap, but see a lot of potential for this to become a larger project down the road. Of course, I'll post any changes I do make here.

Any suggestions?