I have a set of B2Designs 15mm and 20mm hubcentric one-piece spacers for the G35 coupe. I have used these for a few thousand miles before changing my mind on my wheel setup. There are absolutely no vibration issues with these spacers.

$160 shipped for the set of 4 spacers. Add 3% if using a credit card with Paypal.

From the B2 Auto Designs website:
Wheel spacers are made from Aluminum/Magnesium alloy. They are incredibly strong and very lightweight. Now it's time to bolt-on without any swap studs hassles. These are hubcentric spacers that is specifically made to each vehicle; will fitted on your vehicle's original hub perfectly without any gap. Wheel spacers move the wheel out from the hub, effectively widening the stance of the vehicle and lowering its roll center. This simple modification increases lateral stability, which in turn provides improved handling & greater safety. Spec: Bolt Pattern: 5/114.3 Center Bore: 66.2 Thread: 12x1.25

 

20mm spacers have been sold
15mm spacers sale pending

 

Let me know if the 15mm are still available. I'll take them for sure if the price is right.

 

Both sets of spacers are now sold