(Although these particular videos aren't from my classroom, they showcase the science).
Egg in Vinegar
When the egg is dissolved in vinegar, the shell dissolves, but leaves the inner membrane in tact. Besides being cool in general, it's a great example of diffusion - Certain fluids (and small solids) can pass through the membrane.
"Blowing Out" a Candle
When baking soda and vinegar are mixed, they create and invisible gas - carbon dioxide gas (the same stuff you breathe out). This gas is denser than air, and can be poured just like water.
Decomposition of Water
Electric current breaks water into hydrogen and oxygen gas! The salt is to help the mixture conduct electricity. (A lab similar to this is available in my Teachers Pay Teachers store).
Please share any cool or interesting science from your class!