Bitcoin Charts API Data
There's a start and an end that can be quoted, and only one is required although both can be used.

If you want US$ per BTC data from a 24th April until now until now, use:

http://bitcoincharts.com/t/trades.csv?symbol=mtgoxUSD&amp;start=1366784293

If you want all US$ per BTC data until now, use:

http://bitcoincharts.com/t/trades.csv?symbol=mtgoxUSD&amp;start=1279424500

If you want all US$ per BTC data until 24th April 2013,:

http://bitcoincharts.com/t/trades.csv?symbol=mtgoxUSD&amp;start=1279424500&amp;end=1366784293