If you've got the money, get an Alpine head unit - then you can control satellite radio and your ipod (as well as CD and regular radio) through one medium.

I've got the ipod in the glove compartment and the Sirius modulator under the seat.
Its amazing how clean the setup is, all the wires run in the background and you have control of everything from one head unit. People are always amazed when they get in my car.