Techlusion(spl?) makes it. Put one on my old mans street glide. Holy smokes it woke that puppy up. It's nice because you can tune it going down the road. Simple, easy and cheap. He's had it on for over 10k no problems.
There is also the Dobeck Techlusion which is basically the smae thing. You urn teh 3 pots with a screwdriver to tune it. I have no first hand experience with either but my friend has the Dobeck and lovers it.