You can make cool lavas with it. Example: MOIL (Molten Oil). When you cool it down it enters on fire. If you cool all of it down way too much it explodes!
Oh and more a thing: [/set ctype lava 'element'], to make more molten stuff.
Btw, molten ice makes a really nice glowing element..
You can also [/set ctype ice 'element'] To make ice that melts into lava, c-4, ignition cord, glow, deuterium (frozen deuterium yay!), LN2 or even 'none'!