I am posting a year later than others on this topic, but I am just now enjoying the Ruger LC9 with Viridian's R5 ECR green laser sight. The R5 ECR for LC9/LC9s/LC380 is coupled with Viridian's "Reactor" pocket holster, and the combo is a real gem and fun to practice with.
The laser is intensely bright; select continuous or pulse modes via push button on the laser unit, which mounts onto the trigger guard and butts up against the frame below the barrel. The Pulse setting will give you greatly extended battery life without IMO reducing your shooting performance.
The really cool part of the package is the "instant on" feature... when you draw the LC9 from the holster, the laser automatically comes on (assuming you set the laser to either continuous or pulse mode before you holstered it). A subtle magnetic strip in the holster shuts the laser power off when the pistol is holstered, preserving battery power for when you need it.
The ECR designation stands for "Enhanced Combat Readiness" and this is a feature I very much appreciate. (I frankly rebelled against the notion of having a laser-equipped pistol for fear I would concentrate too much on the laser and not enough on a perceived threat). There's no panic while trying to turn on the laser when the weapon is drawn... it's ready faster than I will be in an emergency. Plus, to check on battery life just draw the weapon; if the batteries are on their last legs, a warning light alerts you. Viridian says the batteries should last for months of in-holster "off but ready" time. I'll try to post again in a few months to relay my experience with in-holster battery life.
Want something other than a pocket holster? The Viridian folks are way ahead of you... their site features inside or outside the waistband holsters by Galco, De Santis and Crossbreed, all with the unique ECR "instant on" feature built right in.
You can buy this Viridian product for about $150 on Amazon or elsewhere; the optional holsters will set you back another $40 to $69 at the ViridianGreenLaser.com website. Don't let the cost of batteries deter you (unit requires two batteries). Ebay delivered eight PKCELL brand batteries for $10. The battery is generic (commonly used in invisible fence dog collars) and identified as type CR1/3N, DL1/3N, 1/3N, K58L, 2LR76, CR11108, 72L76 or KL1/3. These lithium batteries will store well, but don't put them in the freezer.
If your goals by adding a laser to your pistol include an enhanced ability to scare a bad guy off and, if you must, to be more lethally proficient if there's no other recourse, I'd recommend what Viridian has to offer.