Hi,
I'm using GreenForce diamond backups. They are well built lights, multiple O-rings and take CR123 batteries. They are twist on lights. My fiance uses the Intova LED light. Same batteries but uses a magnetic switch instead of twist on. They have proven to be rugged and bright. The magnetic switch eliminates the possibility of flooding through the switch. The beam is a little less focused than the GreenForce but they are half the price. I have included links below.
Tyler
GreenForce - Divelights Buy Intova L.E.D. Torch IFL660 with reviews at scuba.com