Right up there with microwave ovens and PVRs (like Tivo) in terms of 'life changing' is Bose's QuietComfort noise cancelling headphones. Expensive but well worth having for a frequent flyer as they virtually kill the 'roar' you hear on every plane. It's a real killer on a long, long flight like Australia to Europe (20+ hours!). The Bose 'phones make a real difference, bringing a real sense of tranqulity.
Now Bose have a new model - Generation 3 - lighter, more effective and with an optional cellphone interface. The last may be the real winner as sometimes the Bose 'phones are too effective.