I've got an Olight mini 2 Valkyrie on ours. What i really like about it is that uses a lever to lock onto the rail instead of a screw. You can take it off on a second and back on in two.
It also recharges by a magnetic connector.
They are less than hundred bucks and I got mine for about seventy on an Olight flash sale.
Editing to add that the light is super easy to adjust front to rear.
Great thread. Not to high jack it, but what's the recommendation for a good light - no laser needed - for an M&P 9mm Shield 1.0?