Don't get too excited about the SLPs. I've always loved that video 25th posted, but that's the ONLY soundclip i've ever heard of SLPs that was good. The rest of them sound like garbage. Maybe only the originals sound good, loud mouth IIs sound like junk. I'd really like to know because that does sound amazing. I'm a big fan of the sound of Mac mufflers. Here's bentley429's car with h/c/i and a powerdyne. Shorties, o/r x, and Mac muffs. It sounds a lot better in person, but it'll kinda give you an idea. I think it sounds pretty badass, one of my favorites.
http://videos.streetfire.net/video/99bf3481-8c6e-45c7-8626-c6232e62d372.htm
Cherry Bomb is advertising a full line of mufflers now. I'd like to hear some of them. My truck had their "Vortex" muffler on it when I bought it, and it sounds pretty good, and it's still in great shape.