I recently bought these Bose headphones:
Yes, they cost $300. Ouch.
If you travel by airplane more than 1x per year, buy these headphones.
Slightly longer review:
These headphones use active noise cancellation to dramatically slash the volume of loud environments; they work best for continuous, white-noise-like sounds (for example, riding in an airplane). The experience of 4+ hours in the air is completely different when you cut down the noise level. Wearing these, vs. not, is a more dramatic difference in overall unpleasantness, than the difference been first-class and steeragecoach.
Each AAA battery lasts a few flights, sometimes more. You can plug in your media player, computer, etc., or just use the noise cancellation alone.