Recs.
Updated
The QC20 in-ear headphones have effective active noise cancelling which can block out mid to low frequencies quite well, making them great for flights.
SpecsUpdate
Pros
Pro Comfortable
The headphones stay comfortably in your ear. They don't always offer a complete seal but surprisingly, this doesn't affect noise cancellation or reduce comfort. Also included are 3 sizes of eartips to help better fit your ear. Note that these tips have a unique design so you won't be able to use aftermarket tips.
Pro Disable noise-cancelling with "Aware Mode"
You can disable active noise canceling at a press of a button. Aware Mode can be quickly accessed from the remote, which will disable active noise-cancelling and open up the microphones to allow you to hear your surroundings better.
LEDs on the control module will let you know when this mode is turned on.
Pro 16-hour battery
These QC20 has a lithium-ion battery that promises to work for 500 charge cycles without diminished returns. After that it will still work, but won't last as long.
Note that the battery is non-replaceable so when it finally does stop working, you will need to buy a new pair of headphones.