Agreed with Quandl being a good source for financial data. Their APIs are also quite well-maintained. Within Quandl, I've found Zack's to be a good resource.

I work with both Quandl and Zack's pretty frequently, let me know if you're interested in buying large amounts of data from Zack's, and I can perhaps get you a discount from the listed prices on the Quandl website.