I just returned from a cousin’s wedding in Houston. One very effective way I found to make the flight bearable is to carry an Apple iPod MP3 player with a pair of Sony MDR-NC10 noise-canceling earbuds.

The iPod holds hundreds of CDs’ worth of music (without being interrupted constantly by the PA) and its lithium-ion battery lasts enough for a Paris-San Francisco flight. The Sony earbuds cancel noise passively (as ear plugs) and actively through destructive interference, and reduces engine noise to a low hum, so even pianissimo passages in classical music are audible.

Updated (2004-04-02):

I have trouble making the Sony earbuds stick in my ear, they have a tendency to work their way loose. I have switched to a better solution, the Etymotic ER-4P earphones reviewed here.