this is what i use as a bike headlight - http://dx.com/p/ultrafire-th-t60-ha-...-x-18650-57007

i like it and it's cheap, so i bought a 2nd one. the 2nd one has no mode memory and the light is a higher colour-temperature (more of a blue tint).

i've also got an SRT7 - http://www.nitecore.com/productDetail.aspx?id=83

the SRT7 is amazing, but that $30 DX light is plenty "good enough" to strap to my handlebars with velcro.