Are there time-series of Bitcoins in circulation?
Historical time-series of exchange rate:


https://docs.google.com/spreadsheet/ccc?key=0AmcTCtjBoRWUdHJuUE1mUkFxa3A0eHBDQkxZLVVFZmc


Source of the data is the "Raw Data" from BitcoinCharts.com.

The raw data of daily "market cap" is available in json


http://blockchain.info/charts/market-cap?timespan=all
http://blockchain.info/charts/market-cap?timespan=all&amp;format=json &lt;-- Thanks to Ben's comment below.