Paint a bullseye on everything - Leapers UTG Instant Target Aiming BullDot Green Laser

It is what it says it do, a laser with an extra lens that widens the beam for quick-n-dirty target acquisition. Great for any situation where accuracy is secondary to speed. Good for choked shotguns and Mini-14s. The elevation and windage knobs are great for getting that green dot concentric with your red dot. Also great is the choice to power it with CR2 batteries instead of CR123.

There's a limited illumination factor, it's not a green flashlight, so I wouldn't count on it to replace a weaponlight. I also wouldn't count on any crims you point it at to wet their pants in fear, as in the advertising picture there, but it'd certainly blind them if you got it in their faces. That said, an adjustable collimator for diffusing the beam into a flashlight-type cone would be handy.

The package says "300 yards range", but I think it's less effective the further out from 50 you go. But that's plenty for the kind of thing you'd need it for anyway.