There's nothing like soaking up some free solar energy, but the biggest barrier to entry has been the expensive devices you'll need, such as solar panels and water heaters. Now you can make your own solar water heater for less than five dollars, and the Instructables site says it's not all that difficult to do.
Just snag the coolant grill from an old refrigerator that you might have lying around, or maybe visit the local redneck section of town and there might be one sitting in the yard. It takes about three hours to construct the device after you've found all the necessary parts, and then, before you know it, the water coming out of that grill is hot enough to burn you. If that water's had time to sit in there for a while and it's a sunny day, that is.
One problem with this idea is when water is moving through that grill, it doesn't get quite as hot. Also, you'll have to take your showers and use hot water only on sunny days. The water heater's creator admits this device is probably only good for camping or for a science experiment, but it's a good demonstration of the simplicity of solar energy. [Instructables, via Tree Hugger]