quattroforum What it says on the tin - UK based quattro forum by the users, for the users.

Audi Fans.com - subscribe to the mail list.

AudiWorld Forums Great Audi forums - very useful.

Audi quattro parts

quattro owners clubUK Ur quattro owners club with info and forum

Martin Pajak's quattro pages Canadian enthusiast site

SJM Auto-Technik Good info here - especially on the injection system.