Steve Spangler Science http://www.stevespanglerscience.com/experiment/00000076 gives a pretty good description on how to make a Vortex Launcher.
Just after Halloween is the time to buy a fog machine. They get very hard to find by spring and you will need to pay a fair bit more to buy one.
Smaller vortex launchers like the Zero Launcher are pretty cool too. http://www.amazon.com/Zero-Toys-Launcher-BLUE/dp/B000FK5JR4