Audi Performance Parts Vendors

I recently purchased a 2000 S4 and was looking for some vendors that sell Audi Performance Parts. If anyone could point me towards some websites where I can find some catalogs that would be great.

Thanks.

try Hartmann-Motorsports.com
I'm not sure if they have a catalog but if you read the May 2003 issue of EuroTuner you would agree they are one of the best tuners. I had a chance to go check out their shop and took a first hand look at their Cover Car a 450 horsepower 2000 S4 it makes 500+ at 100 octane fuel.
I'm taking my new A4 their once the money rolls in for sure. hope this helps.

APR (http://www.goapr.com)
LLTEK (http://www.lltek.com)
TAP1 (http://www.tap1.com)

Try those..