I just replaced the rotors and pads on my '05 A6. I am now a huge fan of the Zimmermann coated rotors. These don't rust, so the entire assembly just looks really clean behind your wheel.
On the advice of others, I paired them with Wearever Gold ceramics from Autozone. Yep, Autozone. After bedding in this setup I've been really impressed. $270 for the whole deal.
I bought the rotors from Amazon.
Zimmermann coated front rotors, 321mm, Amazon $123.86
Zimmermann coated rear rotors, 302mm, Amazon $81.83
Wearever Gold ceramic pads, front, GNAD 1359 $34.40
Wearever Gold ceramic pads, front, GNAD 1108 $28.67