For a long time, I carried the Surefire 6P original black aluminum xenon light.
http://www.thefirestore.com/store/product.cfm/pid_5635_surefire_6p_led_high_output_flashlight_black/
This one at the link is LED but mine is xenon, and was less expensive. They look identical. I still have it and it still works fine. I've moved it over to a flashlight holder on my radio holder strap.
What I replaced it with on my belt is the Surefire G2LF. It's the same form factor as the 6P.
http://www.thefirestore.com/store/p...f_fire_rescue_2_cell_nitrolon_led_flashlight/
What I like about it over the 6P are that it's lighter (due to the yellow polymer body), it's brighter (due to being LED), the batteries will last longer (again due to being LED), and it has a cool-looking yellow body with little Scotchlite reflective bits on it. Actually, the reflective bits come pre-cut on a sheet and it's up to the user to apply them. I applied mine just like in the picture, but there were twice as many as were needed, so I took the extras and put them on a yellow Surefire G2 (
http://www.thefirestore.com/store/p...ackjack_helmet_mount_flashlight_holder_combo/) that I have on my helmet!
When it comes to lighting, I believe in being over-prepared. All three lights I've mentioned are either the original Surefire 6P or a variation of it. They all use the same kind of battery (two per light), the CR-123. I have six extra batteries in a sort of canister designed expressly for that purpose (
http://www.thefirestore.com/store/product.cfm/pid_2158_surefire_spares_carrier/), which when I do EMS I do
not have on my person but in a personal bag on the ambulance. When I do fire (still only in training), I will be bringing that spare battery can in a turnout pocket. In general, I always have at least two lights on me, including the G2LF on my belt and a penlight, with the possibility of having up to four including the G2 on my helmet and the 6P on the radio strap.