Wikipedia's Manual of Style has no shortage of rules when it comes to writing about cold hard cash. For instance, except in situations where it is obvious, Wikipedia editors are supposed to use the full abbreviation on first use in an article: "US$1", not just "$1".
Most currency signs go before the amount. Country-specific articles should use the currency of that particular country, and editors should wikilink to articles about foreign currencies that their readers might not be familiar with. For non-country-specific articles, use U.S. dollars, euros and pounds sterling. Do not capitalize denominations ("dollars", not "Dollars") and use periods for decimals, not commas.
It's also not a bad idea to include conversions when discussing lesser known currencies. It sounds complicated, but this template converts foreign currencies to U.S. dollars automatically. Handy!
This wraps up our numbers talk. Next week, we return to dealing with broader concepts.