Two very nice demonstrations:
1. Hold two strips of paper, each about
5 - 10 cm long and 1 - 2 cm wide, in front of your mouth
parallel to themselvs and to the floor.
Blow between the sheets of paper. The far ends of the pieces of paper are forced together!
2. Hold your head back, blow straight up into the air,
you can balance a ping pong ball on the column
of air (for those of reduced lung capacity, a hair dryer
will suffice but it looks much cooler if you are providing
the air power manually)