[Quandl][1] is free for end-of-data data and of very high quality, but intraday is paid. If you need free intraday data (1-minute or 1-hour intervals) you can try [firstratedata][2] 

TickData.com has the highest quality tick-by-tick intraday data but is very expensive and needs to be purchased separately for each ticker symbol. 


  [1]: https://quandl.com
  [2]: https://firstratedata.com