Efficient Thermoelectric materials  

TransMaterial has a post on Thallium-Doped Lead Telluride - the most efficient thermoelectric material yet found. The post talks about capturing waste heat from car engines, but presumably it could be applied to cogeneration schemes as well.

Thermoelectric materials convert waste heat to electricity without pollution. Given the rising cost of energy to run cars, power generators, and heat pumps, the scientific community has been scrutinizing these materials with increased interest. The average automobile engine, for example, wastes up to 60 percent of the power it produces in the form of waste heat.

Dr. Joseph Heremans of Ohio State University has recently developed a thermoelectric material that outperforms the previous leader by 2:1. Entitled thallium-doped lead telluride, the material promises to make cars and other engines more efficient by capturing waste heat without the use of moving parts. Moreover, it operates best between 450 and 950 degrees Fahrenheit, which is a typical temperature range for such engines.

According to Heremans, "The material does all the work. It produces electrical power just like conventional heat engines - steam engines, gas or diesel engines - that are coupled to electrical generators, but it uses electrons as the working fluids instead of water or gases, and makes electricity directly."