This is to all you canadians:
HAPPY CANADA DAY
ok, now I answer the question.
I think the simplest explosion you could make is as follows:
Make an astable multivibrator (it can be done with a 555 timer), and connect 2 LED's to it, one representing each state of the multivibrator (on and off).
Now replace the LED that lit second with a relay. This relay will be connected to a working very high voltage battery.
Now as soon as you turn the circuit on, the circuit waits for a certain amount of time, then it will turn the relay on, and close the other end, creating a SHORT CIRCUIT in the high voltage end. and what does this mean? maybe a gigantic fire, or a LOUD POP!