In reply to Co1in H: Alpkit ones are over-rated, I've had several issues both mechanical (battery case breaking, a faulty strap) and electrical (torch that won't turn off) and I won't be buying another. If you can't rely on it, it's not worth paying for or carrying.
I have used an Energizer torch for a while (this one:
http://is.gd/wI3Pr4) and have been very impressed so far. Very bright, batteries last ages, well-made, takes up very little room, one big button which is easy to use in gloves but quite stiff so doesn't turn on in your bag. Well worth considering.