Just slip ons? You don't need anything per se. If you change out the A/C then you would need some sort of fuel management or download, but just slip ons then you don't.
I went with the Kuryakyn Crusher slipons. You don't need to add a black box tuner or use a dyno (both very $$$). The stock ECU will adapt. Keep in mind that when it adapts, it will still be lean because that's how HD sets them up to satisfy EPA. I added the 13.8 XiED's from Nightrider.com to fool the ECU into running richer at steady throttle and it works great both to cool the motor and to smooth out the idle and the power band. In fact, I was able to add a K&N direct replacement air filter as well and still not run lean because the XiED's help with more fuel in the fuel/air mixture. Cheap solution to a great sounding and smooth running ride Try it!