I don't think you can go past CES's system. I didn't get one from them and I know my car is very loud (but very unrestricted). Mine is just a 3" split dump pipe system with hiflow cat, hotdog resonator and cannon (with removable silencer makes it much quieter).
The CES system that a few people have bought comes with a 3" split dump pipe system with cat, resonator and a twin tip magnaflow muffler and it is much quieter and doesnt have the annoying drone. And because of the research etc that CES has done, they are pretty good flowing too (not too restrictive and dyno proven).