Another important text was Marshall Sahlins “Stone Age Economics” (1972).
Georges Bataille “The Accursed Share” is another landmark work that develops the notion of “Potlatch” and the excess in gift economy.
A lot of it comes from the field of antropology. I am sure there are many secondary texts out there as well.
Another good place to start is at the Wikipedia article for Gift Economy
http://en.wikipedia.org/wiki/Gift_economy
Hope that helps.
]]>