Subject: What's an easy reaction to create Oxygen gas?

I am currently a senior in high school.  As a Chemistry student last year, I 
had the good fortune of learning from an excellent teacher; one who sparked an 
interest in me to continue with Chemistry this year.  However, due to 
unfortunate circumstanses, this teacher left my school early this year, and 
while we have a replacement, there are still many aspects of the program that 
are lacking.
For example, each year in the spring all the classes would do the "water 
rockets lab."  It was a fun exercise that essentially used the combustion of H2 
and O2 to propel the bulb of a pipet upwards of twenty meters.  The two gases 
were created in separate test tubes fitted with small nozzles, and the bulb of 
the pipet was filled with water, than placed over the nozzles to allow the gas 
to displace the water.  The gases within the bulb were then ignited.
I have decided, out of respect for my previous teacher and with the consent of 
my current one, to perform the experiment with the current junior class.  I 
know how to set up the equipment, and I know to use a reaction between Zinc and 
3M HCl to create H2.  However, I do not know how to create O2 effectively.  I 
need a simple reaction, like that for H2, that can be performed in a test tube 
and uses somewhat readily available substances.  Your assistance would be much 
appreciated, and I thank you for your time.
~Bryan

Re: What's an easy reaction to create Oxygen gas?