Not a whole lot as far as mods yet but I'll list what I have done:
-17x8 MB Weapon Wheels 42mm offset
-235/45/17 nitto nt555 tires (very sticky, love these tires)
-home made ram air intake to a k&n filter
-titanium lugs
-red ambient lighting inside the car
-red alacantra suede shift boot
-ddm tuning 4300k hid kit
-nokya yellow drls
-carbon fiber roof spoiler
-shifter cable and base bushings
-skunk2 short shifter

I think the new tires and rims set the car off and give it a very aggressive look and I love the way the 235's fill the wheel well. I just detailed my car before this and it was my first time trying out all the new 3M stuff I bought and i really like their products so far. Hondata is the next plan for the Si. Hope you guys like it! Enjoy

Also, a big thanks to Jason at Tintmasters for all his help and suggestions on tires. Couldn't be happier with my set up!