I've never tried the grip-type lasers; I don't want anything between me and the already-very-chunky Glock grip.
Another option is the rear-sight laser from LaserLyte. I have one of those on a G26; it works as advertised, but I don't like it all that much. It makes the gun look like it has Mickey Mouse ears, it's not very quick/easy to turn on and off, and it prevents me from installing night sights, which I generally prefer.
"That means that no matter how we reform health care, we will keep this promise to the American people: If you like your doctor, you will be able to keep your doctor, period. If you like your health care plan, you'll be able to keep your health care plan, period. No one will take it away, no matter what." – President Obama, AMA speech, June 15, 2009.
see 13:20 - 13:58