I recommend Lasermax internal guide rod laser. It is a red, pulsating beam. I believe Crimson Trace and Lasermax make grip lasers. I prefer internal as the gun's grip isn't changed and it works in any holster. I too, use Blackhawk Serpa holsters.
Lasermax does make a green laser, that can be seen in daylight and it can be adjusted. It is very low profile and rail mounted. BUT you will have to switch from Serpa. I bought a leather holster from Galco that will accept it and even a light. But, I prefer my locking Serpa for OC.