At first sorry for my english. I hope that you can understand what I want to write.
Frezer - if electrified then its cool (if no energy then back to normal temperature) (indestructible) Heater - if electrified then its heat (if no energy then back to normal temperature) (indestructible)
Solid Hot and Cold elements would be nice, permanent fixtures like Diamond that do not disappear and turn anything that touches them to their own temperature. .. It might be unwise to make temperature changing so easy, though. It might ruin some of the fun.
Also, ANY type of element that is a gas at cold temperatures and a liquid at room temperature, and a solid at higher temperatures would be extremely nice. This way there would be an interesting way of moving heat similar to wax.
...An element that grows in response to photons. :D Plant or whatsit, doesn't matter.
Foggy glass, that absorbs photons and keeps their heat. For greenhouses maybe.