I am planning to create a stock based app for iPhone. It's going to be a paid app. So I wanted to know what options do I have for getting the data from API. I have heard of Yahoo finance API, but think it is not free for commercial use.
What does Apple use for their native app. Could you please provide me with other options.
For historical data (historical stock quotes, historical financial statements, historical dividends, etc), you can use the APIs at http://www.mergent.com/servius
(EDIT: The API can deliver historical ratio information such as P/E ratios, but that feature is still undocumented - will be documented soon).
(EDIT: There's also http://www.zacksdata.com/zacks-data-api . By the way, as a disclosure, both APIs are managed by my company).