This is what I use. Cheap and cheerful. Does the job just fine. Use it for trail riding, commuting and even on my 24hour MTB 100 mile trip. Obviously the battery didn't last 24 hours but for the time I needed it in the hours of darkness it was fine.
http://www.amazon.co.uk/gp/aw/d/B00SFCLIK6/ref=mp_s_a_1_3?qid=1447152287&sr=8-3&pi=SY200_QL40&keywords=cree+lights&dpPl=1&dpID=51bd6ohrh1L&ref=plSrch
I'm going to buy another soon. So far I've used this on my helmet, which I attach with elastic bands, but want another for my handle bars, not because 1 isn't bright enough, trust me it is, but because it means I can point the handlebars light in the direction my bikes pointing and use the head lamp to see where I'm looking. Makes all the difference.