I've been shooting from helicopters and airplanes for more than 30 years and I know there is no substitute for dedicated helicopter mounted, gyro stabilized systems. That being said, there are quite a number of ways to help yourself, including camera selection. First, a good pilot in a smooth ship makes a huge difference. Helicopters will produce better footage if you fly low, though fixed wing aircraft can yield great results when at higher altitudes (say above 1,000 feet or more on wide shots.) Flying in the early morning before winds have picked up also really helps.
With regard to camera selection, rolling shutter is a big problem when there is lots of motion. All CMOS cameras seem to suffer from this problem in one way or another. I've compared both professional CMOS and CCD cameras, DSLRs, GoPro, and consumer grade video cameras. All will produce better results with gyro stabilization and smoother flying.
If you live in an area with good professional video rental houses, you can get something like a Tyler Mini Gyro to greatly enhance the smoothness of the video. If budget is of concern, I've had good luck mounting a DSLR on a mono pod which I've set on the seat cushion of the aircraft to isolate the camera from vibration. Shoot as wide as you can to slow the motion down as well.
One really critical issue is the shutter speed you choose. If you have a camera that can shoot 60 FPS and you can play the footage back at 24 FPS,
it will yield a slow motion effect that really helps smooth vibration.
If you have a chance, you might view this video I shot last month and watch the aerials carefully.http://www.youtube.com/watch?v=j-xCALXBUAI
We hit a really bad windy day and the helicopter was slammed back and forth constantly. I was using a Tyler Mini Gyro and a large Panasonic professional video camera. Even so, the footage was too bumpy to use as it was. I had to stabilize the footage in Adobe After Effects using the "warp stabilizer" function. It did an excellent job, but if you look closely, you will see momentary blurring as the camera shook so violently that there was motion blur in the captured footage.