i need a chemical reaction which (if possible) would normally take place at high temperatures but, with the addition of a catalyst, takes place at room temperature (or as close to it as possible) and is easily demonstrated in a lab.

any suggestions?

hydrogen peroxide decomposition. google "elephant toothpaste". you can also see an example in my youtube video at http://www.youtube.com/hermanntrude it's in the video on decomposition reactions.

ok thanks, are there any others while i'm at it?

cant think of any right now. many reactions are catalysed by acid or base... I guess ester formation might be an example... also some reactions are "catalysed" by light.

Hm, how about the reaction between sodium metal and chlorine gas? It is quite slow but a drop of water will make it go like crazy.