One of the most compact green laser sights i've ever seen - Crimson Trace CMR-203 Rail Master Green Laser Sight - Universal

I mounted this on my KSG 12 gauge shot gun. After about 25 slug and 00 buck shot shells fired with it on the gun it still held it's point of aim. The green laser is very bright, and can be seen in the bright sun, were as my red lasers become almost invisible in that kind of light. I like the on/off switch that you only have to tap on either side to active/deactivate the laser. It has a good solid mounting system with adapters to fit most weapons.
Pros: Small, light and compact. Very bright green laser
Cons: High priced

This review was written in the old system and had content requirements that are different than reviews written today.