One of my hobbies is cave diving
, I've got lights out the wazoo, everything from a 50W HID to handheld backup lights, I've got two backups mounted on my helmet for doing things hands free like tieing into the mainline, surveying etc. Helmet mounting is probably ore than you want to do so I'd suggest a mask light.
Look at the "mini light" on this page it's good for mounting on a mask strap, I have to assume you would be wearing a mask, wouldn't you? If you could find a waterproof headlight, not so sure how that would work with a mask. I would stay away from leisure pro, it's sort of like Walmart.