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incrediBILL - 12:00 am on Aug 21, 2007 (gmt 0)
They exist and are called the YAHOO directory and BOTW directory, but the fees are not nominal.
A general listing *might* work if (1) it charged a nominal fee, say $15 a year - that would keep the fly-by-night sites out, and (2) if there was some kind of ratings where people could rate sites based on 3-4 factors.