Headphones usually have a range of about 20Hz to 20kHz, so it's supposed to be enough for most applications. A sub-woofer can go also to 20Hz or less, but they are not specially cheap in that range. But, is there more?
Some reports say that certain people can hear higher frequencies than 20kHz. Hearing changes with age, with more probabilities to lose especially this high-pitch range. Also, in different stages of the life, the ear system could be exposed to high decibel pressure, almost surely creating permanent damage.
Some hearing tests like to set up the top range in 22kHz. A sound of this frequency should be distinct to every other, and the user must press a button to ensure that he or she hears it! A difficult task because 16kHz is already out of the normality. The 88th key of the piano has 4186.1Hz so it's four times more...
Anyway some creatures do have an incredible ear system, with dogs as nearest ones with a top limit of about 45kHz.