I have a Streamlight TRL-1 that is working very well for me on my Glocks. I've run about 400 rounds through several Glocks with the light mounted with no problems to date (light OR gun functioning).
The Streamlight compatibility list states the TLR-1 can be used on the PX4 Storm pistol with the standard Glock locating tab (that comes installed on the light when you buy it). Here is a link to the compatibility list (see page two for Beretta models):
And a link to the light itself:
You can pick these up on Amazon for about $100, plus tax (free shipping). MidwayUSA.com also carries them, as do a long list of other online vendors.
I'm not connected to these companies in any way; just a happy buyer/user.
Current home defender set-up: