I just recently bought an IS220D a few months ago and couldn't wait to add a few modifications to it. First thing I bought was a tuning box from TDi Tuning, they thought they could only alter the fuel injection on the IS until the looked under the bonnet, turns out there was a connection to the turbo too.... bonus. They claim it would have approx 220BHP and 470NM torque. As soon as it was installed and I took it for a test drive with them, the difference put a huge smile on my face. Slightly less turbo lag under 2 revs, but the torque is amazing mid range.
Although it's not a modification, I seen so many posts about the EGR, so I had that taken off and cleaned. It was pretty packed up with carbon, the car had only done 65,000 miles.
Then I bought H&R lowering springs, they said 35mm drop, seems like more to me but I didn't measure. After installment, the ride is a little firmer, I can fell speed bumps and pot holes more than I did before. But far less roll going around the corners and the car looks far better.
And recently had my windows tinted, not fully dark, I don't want it to look to much aftermarket, I also had the front windows tinted to a just legal shade.
I am looking at alloy wheels next, most likely 18 inch lexus wheels. Currently have really ugly 16 inch lexus wheels. Previous owner sprayed black.
What do you have?