There are lots of Cree torches that are good.
They take those Li-ion 18650 batteries and can last about an hour on each battery.
I’ve lost all the details of the specific torches, but I’ve posted them on here before so it might come up with a google search (longer than a year).
Basically you can get the torch, 2batteries and a charger for about £35. Then you can get a new torch later as the LEDs develop for about £12.
I just use elastic bands as my helmet is quite a torch-friendly shape, but some people use the Exposure Joystick mount – there will be posts about which torches fit precisely in it.
Other options:
Stump up for an Exposure
Buy a bar mounted XM-L bike light that comes with a head mount. You can store the battery pack in your backpack. This is probably the easiest way to get max power and runtime (£27 from ebay).