The Soviet nuclear lighthouses discussed at Dinosaurs & Robots were powered by the thermoelectric effect - my current professional field.
Thermoelectric devices use electrical power to move heat, or use the movement of heat to produce electricity. The vast majority of thermoelectric devices sold today are for cooling; they can chill something to below ambient temperature (which you can't do with a fan) and they can be made much smaller than a compressor-based refrigerator.
In the early days of thermoelectricity, however, the main interest was power generation. As early as 1961, NASA launched a satellite powered by a Radioisotope Thermoelectric Generator. It's easy to forget that radioactive materials are said to be "hot" because their temperatures are high, even when they're just sitting there. Such materials are used to heat one side of a thermoelectric device, while the other side is cooled by fins. The heat flowing through the device is converted (partially) to electricity. The Wikipedia article linked to above lists the RTGs used in those Soviet lighthouses.
Thermoelectric power generation has experienced something of a renaissance since the early 1990s, when funding from U.S. military R&D programs brought more academics into the field. Today, as we face declining world oil reserves, energy efficiency is once again on the public's mind. TEs are a leading contender, for example, among proposals to make use of the waste heat coming out of your car's tailpipe. BMW built a prototype last year.