The Streamlight TLR-4 will almost line up with the front of the gun. It is a little lighter than other options, and much more affordable
The Streamlight TLR-2 is a more durable unit with more run time, but it will stick out in front of the barrel (a look that I like).
The Surefire X400 and the Viridian X5L are higher end and really expensive.
Duty guns rarely have lasers mounted. Most are using TLR-1s or X300s. Holster options for any of the above are very limited if existing at all. Most laser/light combos are used for home defense, and if so, too bright of a light in a house interior can be a problem. If it is a HD gun with no duty requirement, either a TLR-4 or TLR-2 should do the trick. The TLR-2 comes with a green laser option, which is more visible than the red in various conditions.