I ran across the website this morning. It provides sound samples at various frequencies to see what you can hear. It's definitely not a true scientific test, but the results will probably surprise you. I can't hear any of the sounds above 15kHz. Might be interesting to start a poll.
http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearing-test/
http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearing-test/