How much are you looking to spend?
I have a Lasermax guiderod laser for my M&P 9. If you get them from Lasermax, they run about $300 (plus shipping). You can also find them on Amazon for a bit less.
(I like Lasermax due to the fact that it is factory set and aligned with your barrel, no need to adjust it)
Insert witty comment here......
Vincit Omnia Veritas
Vincere est Vivere