looks like some of the options that pop up are:
Borla XR-1, available in 3.5",seems there are lots of types, and some of the prices are up into the 300-400$ range which is alot considering other types sell for 100-200$, but they seem to use steel wool packing instead of fiberglass, might last longer.
Raceing beat, not available in larger than 3",
Vibrant resonators, Aaron Cake said he had some success with their "ultra silent" style resonators however these are not available in 3.5" they do make a traditional bottle stye resonator in 3.5".
http://vibrantperformance.com/catalo...oducts_id=1703, very cheap at 100$, need to look into this option more.
the borla's seem to be the most recommended but the type/part number isn't usually mentioned