Wow, this is an I can't sleep reply.
Anyway, most of the mods I have done are superficial, just one performance mod. Here's what I have (all factory/OEM):
ASpec body kit w/spoiler (about $1000 all in, but can be purchased separately)
fog lights ($260)
TL Aspec rims (18") ($1000)
Comptech (now C-T Engineering) icebox (cold air intake) ($150)
USASpec ipod adapter ($120)
And as for the tires, ditch the OEMs, I heard/saw reviews that they suck. I got Bridgestone Pole Positions, which are supposed to be awesome, cheaper, quiet, and handle well:
Bridgestone Potenza RE960AS Pole Position
Good luck