good sounding comfortably loud that can still be tolerated in the neighborhood as long as you aren't screaming down the street. Would probably go with Muzzy's or Micron. If you just want LOUD, then D&D.
Haven't really tried looking for them since they are much louder than what I want ( I actually still get along with some of my neighbors and usually leave the house around 0400 for PT). Could try parts411 though?
Hindle does make very great pipes, but for the money I would get the full system and all its perks. With just a slip-on, you can be "cost effective" in your search and still get what you want.