Where to get historical intraday trading data from?
I work at Quandl and we have intraday data here: https://www.quandl.com/vendors/as 

The databases include S&amp;P 500 One Minute Bars, NASDAQ 100 One Minute Bars, Dow Jones Transportation Average One Minute Bars, Dow Jones Industrial Average One Minute Bars and Dow Jones Utilities Average One Minute Bars.

The databases cover five years of history and include OHLCV data and all additions, removals and changes to the index. 

You can use our API with every dataset. Each database has a section explaining API usage and bulk download. You can also check out our detailed API documentation here: https://www.quandl.com/docs/api

Hope this helps!

Also, we apologize for the shortcomings of our site's search features - we are working very hard to improve this to better help users find the data they need.