Need something unique for the open source Linux-loving GNU-spouting Free Software Foundation member in your life? ThinkGeek has the answer in the form of commemorative open source challenge coins. They will contribute to the open source cause and might even get you a free drink.
Military history contains a rich tradition of challenge coins. These small medallions bear an insignia and are carried by members of specific organisations. They are so named because they prove membership when challenged.
They also can raise morale, giving members a sense of bond and belonging and camaraderie.
ThinkGeek has crafted its own  for open source lovers worldwide. It comes in two forms with Linux/GNU and GNU/FSF variations.
The price is $US 19.99 with $3 donated from each sale to the Free Software Foundation.
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UPDATE: Available here: http://osstore.com