Watch out for an A320 addon soon to be released by a company called AirSimmer. Will work with MSFS 2004 and aims to be the most complete and realistic A320 addon ever. All systems will be simulated including realistic failures and ECAM drills. I have reason to believe it based on conversations with the developer.
If it can equal or beat the Flight 1 ATR-72 and the PMDG 747, it could be good!
Nothing has come close for the moment. Apart from the Level-D 767