Midwest Engineering and Design 
Sell plans for such items as underwater camcorder housings, 1 and 2 person submarines, hydrophones, ultralight aircraft, scuba tow scooters, and pulse induction metal detector.
http://www.angelfire.com/ks/diyplans/index.htmlAffordable Submersible Products
Plans for an underwater video camera housing, lights, and a waterproof keychain laser pointer by Gary Dagastine.
http://members.tripod.com/econosub/
Scuba Tow
Build it yourself diver propulsion vehicles (DPV) plans for the scuba tow and a one man submarine.
http://www.scubatow.com
Scuba - do it yourself
Reinhard Kopka's site dedicated to homemade diving equipment and accessories. Plans range from lights and dive computer interfaces to diver propulsion vehicles and rebreathers.
http://insel.heim.at/malediven/350052/english.htm
Lunkercam
Plan to build underwater video camera.
http://www.mninter.net/~boardman/
Elfmun Underwater Products
Offers plans, parts, and kits to build underwater canister dive lights and video housings. Includes ordering information, price lists, and contact details.
http://www.scuba-lights.com/
