G'day Toby,
Jr Walks is right. I've got my self a Sony HDR-XR520 with the sports pack SPK-HCE which can give me up to 5m depths of HD recording. You don't have to get the higher end camera like this one but its the housing sports pack thats brilliant. Down side is the housing is clear and lets in light which drowns out the LCD screen (you have a little mirror which allows you to see the LCD screen) and makes it hard to see if your trying to zoom in on stuff, especially since we have kiting in mind and when its sunny, things are not perfect. But the other side to that is because its HD, when you edit the footage, you can post zoom (editing program allows you to zoom footage) and the quality is still mostly there, so you don't have to zoom so much while filming and therefore just 'aim' the camera and record, don't even bother too much with zoom. By the way this camera is 12 times optical, you can fit a 2 times adaptor with a small modification (a small repositioning of the camera inside the water housing to pull its position back and then you can fit a 2x or even wide angle lens).
Also, this camera has brilliant steady shot features which makes it perfect for in water filming of kiting while in the surf. I've checked out other brands and this sony model is the best I've see so far.
One last thing, working is full HD is hard on you computer, you need a fast powerful computer to handle the extra info, my software and computer was fine on my older Standard Definition stuff, but ****s it self now on HD

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cheers,
Robert.