When thinking about e-currency in a general sense, what features discourage black market usage, but promote anonymity? I'm interested in e-currency that discourages black market usage (child porn, meth deals, etc) but allows for anonymous operation (donations to charity, buying a pizza, viagra, or other health issues)

What pre-existing work exists that researches applicability of various "controls" into e-currency systems such as e-cash, Bitcoin, Open Transactions, etc.  And by "controls" I mean:


Psuedo anonymous user registration
Usage "escrow" allowing third party audits or reviews of transactions
Anything else that would be resisted by the Bitcoin purist.


I'm interested in any example you can think of, links to Bitcoin Talk, or any other whitepaper that discusses ways to legitimize e-currency to a moderate fiscal conservative.
The issuing of currency by a central authority discourages black market usage in a sense that all coins in the system can be tracked by the central authority - with AML and KYC policies.