Originally Posted by terrier

This is called the Valsalva Maneuver. It is taught to all scuba divers and military pilots (probably should be taught to civilian pilots as well, but I'm not sure it's formally part of any FAA requirement, so some programs may not bother.)

This is the surest way to equalize ear pressure during descent - just be careful not to blow too hard. If your Eustachian tubes are clogged, try tilting your head from side to side as you blow - this can sometimes open them enough to pressurize. Be gentle, though! If you over-pressurize your inner ear you may experience dizziness and/or pain. In extreme cases, you could even rupture your eardrum.

Remember - pinch your nose, close your mouth, and blow gently. You're just trying to get enough air in your ear to equalize the pressure, not trying to blow out your eardrums.

Edit: I guess I should point out that this works during descent but not, for obvious reasons, during ascent.