Ask HN: A question about historical stock data.

Hi,

I have an interesting idea for a web app geared towards investors. However, the web app would require an immense amount of historical financial data. Does anyone know the common way to go about requesting historical stock data?

The web app would also require historical financial data (read: operating metrics) for nearly every public company on the planet. Is there a company that aggregates this data, or would I need to find and parse it myself?

Thanks for the help!