Garmin Virb (discontinued) is what I have, aerodynamic and good video. Gopro has always been a fan favorite and has improved the product line with image stabilization, waterproof with streaming capabilities.
There's also knockoffs available. Lot depends on the features you need. Voice input via Bluetooth or wired mic, 360* views, etc.. You need to determine what you need and your price point.
I found battery life to be a large limiting issue. With my 08, since I already had a wired headset I ran a USB power cord up to my helmet for the camera. Since I really tended to use the camera as a driving dash cam and not as a travelog I went to a wired front/rear camera system on my 18 for safety/insurance reasons.