Artificial Gills at a Wal-Mart Near You!

An Israeli inventor, Alon Bodner, has made a working prototype of a device that lets divers breath the dissolved air in the water, without a need for tanks.

From the article and interview at IsraCast:

"The system developed by Bodner uses a well known physical law called the "Henry Law" which describes gas absorption in liquids. This law states that the amount of gas that can be dissolved in a liquid body is proportional to the pressure on the liquid body. The law works in both directions – lowering the pressure will release more gas out of the liquid. This is done by a centrifuge which rotates rapidly thus creating under pressure inside a small sealed chamber containing sea water. The system will be powered by rechargeable batteries. Calculations showed that a one kilo Lithium battery can provide a diver with about one hour of diving time."

This means that the time you can spend underwater is now determined by the battery, not the tank capacity. It's an improvement because batteries are likely to get much better, while compressed-air tanks are pretty much as developed as they're gonna get.