Required:
Jérôme Blanc, "Free Money for Social Progress: Theory and Practice of Gesell's Accelerated Money," American Journal of Economics and Sociology (1998), 469-483 [JSTOR].
Eric Helleiner, "Think Globally, Transact Locally: Green Political Economy and the Local Currency Movement," Global Society 14:1 (Jan. 2000), 35-51 [IUB On-line Journals].

Further Reading:
Edgar Cahn and Jonathan Rowe, Time Dollars (1992).
Benjamin Cohen, The Geography of Money (1998).
Rachel Tibbett, "Alternative Currencies: A Challenge to Globalisation?", New Political Economy 2:1 (1996), 127-135 [IUB On-line Journals].