Flip cameras generally produce pretty good video and sound quality, however you'll struggle with fitting it to a bike or helmet. On top of that they're not shockproof in the event of a crash, or waterproof in the event of rain showers.
If you're not looking to spend much then maybe the Dogcam HD will be to your liking? Very small form factor, 720p HD video recording (same as the Flip). Sound and actual video quality isn't quite as good as other options, however at around £99 (I believe) it's the best deal I'm aware of.
There should be Dogcam HD footage previews on YouTube if you're interested.
Edit: Magnatom has a review of the "Wide" version on his blog, and possibly the regular version as well. The wide version is slightly more expensive.
Link!