Tech Articles and Product Write Ups:

Tracking/Racing the Audi A4/S4

Heel-and-Toe Solution

Even though this is written by BMW, still very good.  How to drive the Ring

Audi S4 Engine

Power Bleeder European Car Review

Bilstein PSS9 Dyno Test Results - must read if considering PSS9s

Dyno Test of StartupRacing GT B6/B7 A4 Exhaust

StartupRacing GT Coilover Kit for B6 and B7 A4/S4

Brembos for a B6/B7 A4/S4