You might want to look at Magnaflow. They also have some sound clips. They sound great when you hammer it, good at idle, but relatively quiet at general cruise. They are a straight through design and boast HP increase.

I heard CaptnBill's car today. He has a dual chambered exhaust. Not only is it chambered under the car as most, but it has chambers where the mufflers were as well. I was amazed how quiet it was. Don't get me wrong, it was still loud, but we could easily carry on a conversation in the car. It was no louder than most systems with mufflers. And the sound was deep and throaty. A really great sounding system. I haven't seen the dual chambers before. Now I have to consider it before I buy a system. I loved it.