I have always been a fan of simplicity. I have come to believe that simple solutions are also often the most elegant as well. Here are two of my favorite ideas which have stood the test of time. These are technologies that work in every place and period of time. That is part of their brilliance.
THE MASONRY STOVE AKA RUSSIAN FIREPLACE
These are woodburning fireplaces designed to burn very hot wood fires. They create very little smake because they burn so hot (1600 degrees Fareheit or hotter) and are said to be 90% efficient. They burn with the air supply and chimney damper wide open. This results in a clean burn, with little visible smoke. The distinctive feature of the heaters is a series of baffles to pull the heat out of the exhaust. The masonry absorbs the heat of the fire, then radiates it gradually back into the room. Masonry stoves have been widely used in Europe and Asia for centuries. The stoves provide clean combustion at a high temperature to avoid pollution and creosote build-up. If you have ever been inside an adobe house in the southwest or a well designed passive solar home anywhere it is the same principle as having the sun shine on a brick floor or a Trombe wall all day and radiate the heat back at night.

The fireplaces are usually massive (that's the point after all) and some are amazingly beautiful. Since wood is a renewable resource and these use quite a bit less than you might imagine given their size because they burn so hot we may well see more of them again soon. They had a brief resurgence in the 70's and 80's but they may be due for another comeback. According to the Masonry Heater Association
The main thing that distinguishes a masonry heater is the ability to store a large amount of heat. This means that you can rapidly burn a large charge of wood without overheating your house. The heat is stored in the masonry thermal mass, and then slowly radiates into your house for the next 18 to 24 hours.
If you burn wood fairly rapidly, it is a clean fuel. If you try to burn it too slowly, the fire will change from flaming to smoldering combustion. The burning process is incomplete and produces tars. Atmospheric pollution increases dramatically. This is important if you are planning an energy-efficient house. The average energy demand of your house will be quite low. For most of the time, it may require only 1 to 2 kW of heat. For most conventional woodstoves, this is below their "critical burn rate", or the point where they start to smolder.
These heaters are meant to be sized for the space they are heating so if you have a small house you will also have a small heater. Just as in a passive solar application, you want the mass to be in proportion.

RADIANT FLOOR HEATING
Okay, those of you who know me knew I could not get through this without at east a nod to Frank Lloyd Wright. Radiant floor heating is not a new idea. It is, in fact an ancient one. It was old hot when Wright introduced it to his homes in the 1930's. Wright went to Japan to work on the design of the Imperial Hotel in Tokyo. In 1923 he was invited to the home of a nobleman who had discovered Ondol in Korea and could not forget it. After returning from Japan he had an Ondol room built in his home. "The indescribable comfort of being warmed from below" impressed Wright.

A traditional Ondol floor heating system conducts the flue gases of a fire (traditionally from the kitchen where the fires were kept going for cooking) under the floor of a living space. Horizontal flues passageways for heat and smoke ran beneath the room's floor, connecting the fireplace and the chimney. Hot air from the fire passed through the flues and heated the stone and mud floor. Wright invented modern radiant floor heating, using hot water running through pipes instead of hot air through flues. From the meeting of Eastern and Western architecture came a true hybrid heating system.
The Romans had a similar idea, a bit more complicated but still in the realm of simple, elegant solutions.Instead of a fire in each room, Romans had a special fire room built against an outside wall. The floors were raised on pillars and the walls of the villa were hollow. The heated air from the fire went to all the other rooms, through these spaces under the floor and in the walls.

This is a picture of the hypocaust at Rockborne in Hampshire. These pillars (red) held up the floor and allowed the hot air to circulate underneath, heating the room.
SIMPLE AND ELEGANT
PERHAPS SLIGHTLY IMPROVED WITH NEWER BUILDING TECHNOLOGY BUT THIS IS DEFINITELY NOT ROCKET SCIENCE