I am in the same delimma. I have a 2002 I35 and I am looking to get some aftermarket wheels for my ride. Problem is, there are not to many luxury wheels on the market that provide class, style, and best of all subtleness. Here are some manufacturer websites you may want to look into if you are really looking at getting some Luxury Wheels for you car.
www.diabloracingwheels.com
www.dazzmotorsports.com
www.giovannawheels.com
www.mhtwheels.com
www.privatwheels.com
www.cecwheels.com
And here are some companies that sell them
www.streetdreams.org
www.discounttiredirect.com
www.discountwheelwarehouse.com
www.exclusivemotoring.com
www.cheaprims.com

Hope you have luck finding the right wheel for your car. (Trust me, its not an easy tasks when dealing with a luxury ride.)
Oh before I forget, here is the wheel I feel looks best on the I35's
http://www.maidowheels.com/wheels.asp
Thats right the Maido GR5.

 

LS5 or MD1 are awesome.. http://www.maidowheels.com/wheels.asp

 

that's a good lookin wheels dude but it's heavy. you gotta take that into consideration. especially if you're goin 18" or larger. it will slow down your car and also in turn will cause your I35 to waste more gas. i would look for a combo of lightness and looks. the wheel that you like i believe is 29lbs a wheel and that's HEAVY... good luck in your search though