You don't say WHY you want a camera. If it's for fun, almost anything will do. If you are being harassed and want admissible evidence and video good enough to read license plates off of speeding cars, you'll have to be more picky.
See: helmetcamreview.wordpress.com
Look at the Tachyon XC. I was interested in the VholdR until I found that it wasn't waterproof. I now think the Tachyon is probably the best bet. $150, uses SDHC up to 32GB, very long battery life, waterproof, decent looking output.
They almost all say 640x480, but that doesn't mean that it's a GOOD 640x480 - I had the original oregon scientific camera, and it was not good. Any vibration caused bad distortion.
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Work: the 8 hours that separates bike rides.