I'm thinking of building a mining machine, and am trying to figure out if it will be profitable. I've used this: http://lorelei.kaverit.org/cgi/calc.py to calculate the profitability based on today's difficulty and compared with today's BTC/USD rate. But I would really like to see how the [BTC/USD rate]/[difficulty] has changed over time so I can try to guess at future profitability. I can find graphs for each (difficulty here: http://bitcoin.sipa.be/ and BTC/USD charts from MtGox), but not the raw numbers. I need to find the raw numbers so I can compare them and make a value/difficulty graph.

Does anyone know where I can get the raw data for difficulty and exchange rate? (or better yet, a graph of the ratio that someone has already put together)

Thanks

Even without the data you can always calculate what would need to be the case to remain profitable, or to remain as profitable as you were at a given difficulty level.  For example, if Bitcoin Charts is right about the next difficulty level, then the exchange rate needs to be at least $1.77 for me to be as profitable as I was at the last difficulty at the current exchange rate, and so on.