Are you just looking for loud or are you looking for performance. Flowmasters are loud but not real good in the performance area IMO.
Check the specifications on a few mufflers and cat-backs before you really decide. There have been many posts on here regarding the different flow characteristics of the different mufflers.
2004 DSG Mach 1 w/IUP 5 speed (Born on Date: 10/09/03)
Dyno - 1/28/04 (1300 miles)K&N Drop-in Filter, SAE - 273.8 rwhp 302.5 rwtq
Dyno - 3/6/04 (3400 miles)K&N AirCharger, SAE - 282.5 rwhp 312.6 rwtq
Dyno 4/22/05 304rwhp 326rwtq