Could you provide also the raw data? I updated this graph every difficulty change:
http://bitcoin.atspace.com/income.htmland now I have a gap since March 26. I started regular download from mtgox but I can't find the data to fill the gap.
I've already developed an application which monitors bitcoin market prices and makes the raw data available.
http://nosoperor-internal.appspot.com/market_datalists all the market data since I started gathering it, quite a few months ago. Recently (last couple of months) it has been pulling and storing data at 1 minute intervals. I've just added some new querying capabilities which allows you to fetch a limited number of data points, limit by start and end date, and filter by market. See details here:
http://bitcointalk.org/index.php?topic=3313.msg90683#msg90683