Do-it-yourself projects and plans for anyone who can swing a hammer.
Making the switch to an on-demand hot water heater make a lot of sense. But if you haven't made the switch yet, save energy and money by insulating your hot water tank. Instructions for insulating your tank are available for the EERE.
Building a passive solar hot water heater is a great idea, too. It's probably one of the easiest do-it-yourself solar energy projects.