TEC (Thermoelectric Cooler) units with preattached leads. When voltage is
applied, one side of a TEC will get cold and the other will get hot (you can switch the voltage to flip he direction of the temperature difference), or you can use them in reverse to generate electricity.

These amazing semiconductor coolers get ice cold in minutes or heat to boiling by simply reversing the polarity. You can be used for them is for temperature regulation of diode lasers, but they can be used for numerous applications from CPU coolers to alternate power sources, or even for your own custom car drink warmer/cooler (power from cigarette lighter).