A familiar item to musicians... but also use in medicine both for hearing tests and to check sensitivity to vibration in neurological tests.

"Tuning forks, usually C512, are used by medical practitioners to assess a patient's hearing. Lower-pitched ones (usually C128) are also used to check vibration sense as part of the examination of the peripheral nervous system."
http://en.wikipedia.org/wiki/Tuning_fork

See examples here, for both purposes:
http://www.medicalexpo.es/cat/medicina-general/martillos-par...

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Note added at 34 mins (2013-04-09 21:59:41 GMT)
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Here's a relevant example from the page just cited:

"Diapasón médico de Rydel-Seiffer
128 Hz | C-128
Made of aluminum alloy and designed to meet medical requirements, the frequency of this tuning fork is designed for use with vibration and bone fracture tests. Weighted in order to assure correct frequency. Made in USA."
http://www.medicalexpo.es/prod/prestige-medical/diapasones-m...