digital cameras are probably the best video quality with the cheapest price new or used. If you gots da money, then usually the more expensive the better
I actually think the video quality on the I phone 4 sucks and it blacks out on the sides. My point and shoot that I paid like $85 dollars for takes better video. I bought a JVC Everio and it works great if your looking for an actual video camera.
Also look for a camera with flash memory rather than a hard drive they are cheaper and you don't have to worry about the hard drive going bad especially bouncing around a lot in a sports environment.
i have a kodak sportplay HD.. it records at 1080p and does fine underwater, plus does good with fast movement.. overall i have no real complaints about it.. Plus its really affordable..